I have a '90 dodge w250 and just love that sucker. It was bought just for a wood/field truck but has become a daily driver. Near as I can tell it's bone stock,maybe a Dana 44 front maybe Dana 60 rear(know rear is floater,did brakes and had my eyes opened 16" tires all around).This is my first heavy truck and I don't know much. Can anyone help me with a best bang for the buck list of getting anything like highway economy?? It's got a 318 and E-check is not an issue around here. Looking underneath duals might be possible but plumbing will be wierd due to fuel tank placement.Don't know what all will bolt on engine. Just dumb I guess.  

Im no expert, but the first thing I would do is a genuine tune-up. It economical and effective

spark-plugs
plug-wires
distributor-cap and rotor
air filter (I reccomend a K&N filter, they flow alot better and are re-useable)
fuel filter
oil change
run some injector cleaner through a tank of premium gas.

After all of that, you could look into upgrading the exhaust.  Id go dual 2&1/2" or  with flowmasters - that should be plenty of flow for a mild 318.  Adding a set of long-tube headers will help even more.

Anything after that your looking at costly, time consuming mods.  You could install a "RV" or "pulling" cam, which are made to increase low-end torque.  You could also change the rear-end gearing and so on.  These will definetly help, but Id definetly do the tune up and see how much it improves first.  

A full size, heavy truck is is going to LOVE gas no matter what, but all of these should help your mileage some.  

figure out where your gonna drive the most. my naughtydodge @6100 lbs and a HEMI was able to go 19-21 mpg with a single 3 inch pipe and a K/N filter only in the box. Taller tire at load range e and pressure at 65-70 psi,yea it road a bit rough empty but the milage was worth it.if you can put a mild hiway tread as you can stand and tall and skinny as will fit you may git 2-3 mpg better..maybe.. happy wheelin!  

try changing the mass airflow sensors two. if its high mileage then it may be beneficial to change sensors.  

Thanx, 150 miles a day commute(we get winter here this is best no *** get there beast in "fleet")For winter it's got beefy's on. Actually have "summer" tires as well. Waiting on warmer weather as I found out as I get older it's not as much fun running hand/wrench under tap to thaw as it once was. Will update as I can. Going to be almost 40 this wknd maybe play then  

well it got the tune-up. it broke down 3/8 during the blizzard we got here(15/20inches all around)so it got rescued away from home and fixed there for more than I would've liked...sigh. so right now looks like it picked up about 2 mpg after. plugs,wires,cap,rotor,under rotor critter,n coil,also oil and lube n proper filter replacements. O2 sensor next up then fix/replace exhaust as can get done.  

If you have not already done so, change all the lubes in drive train(tranny, T-case and axles) and change engine oil often. Run tires at or near max pressure to reduce rolling resistance too. One more thing, 2 1/2 inch duals are a mistake on a engine that size, bigger is not better. Engine actual need a little back pressure for best low and mid range response and efficiency. I would suggest a nice single around 2.5 inch with a flow master or such and it will run better overall that way. If you feel you want the dual sound, use a one in two out muffler.If you do true duals, 2 inch pipe would be best for that size engine as again, bigger is not better here when searching for efficency.  

if the rear cover plate matches outer edge of housing it is a spicer 60 (9.75 in. ring gear) if it is shy of matching it is a dana 70 (10+ in. ring gear) dana 44 had vacuum actuator on driverside axle tube didn't have manual hubs if it has manual hubs possibly aftermarket or another axle model.  What are the gear ratios? depending on ratios you can achieve better fuel mileage such as running 3.28:1 instead of 4.10:1 both chrysler product gear ratios. also running a CDI ignition with your factory ignition can help becausae of increased spark energy While I went to school saw demo on difference between stock and cdi ignitions stock had (orange color spark colder spark/flamefront) and lost power effectiveness as rpm increased from idle however cdi (Blue spark-hotter spark/flamefront) kept spark power as rpm increased. does increase power voutput and fuel economy over stock  

dodgethis:
if the rear cover plate matches outer edge of housing it is a spicer 60 (9.75 in. ring gear) if it is shy of matching it is a dana 70 (10+ in. ring gear) dana 44 had vacuum actuator on driverside axle tube didn't have manual hubs if it has manual hubs possibly aftermarket or another axle model.  What are the gear ratios? depending on ratios you can achieve better fuel mileage such as running 3.28:1 instead of 4.10:1 both chrysler product gear ratios. also running a CDI ignition with your factory ignition can help becausae of increased spark energy While I went to school saw demo on difference between stock and cdi ignitions stock had (orange color spark colder spark/flamefront) and lost power effectiveness as rpm increased from idle however cdi (Blue spark-hotter spark/flamefront) kept spark power as rpm increased. does increase power voutput and fuel economy over stock

90 would not have a vacuum disconnect on axle, that started around 95. Taller gears is not going to help MPG here because that truck does not roll easy and is heavy and taller gears will cause it to strain more and together with current engine setup, MPG would likely get even worse. Part of the problem is the engine size and mods to it because many have trouble understand that big exhausts on a small engine can really hurt low and midrange response, power and efficiency. And again as stated earlier, taller gears with that combo would make MPG even worse and give it slug like performance too. Forget the fancy ignition and loose the big duals and get a little back pressure behind that engine and advance timing some and use 89 octane fuel too (Dodges were really bad about retarding spark to tolerate 87 octane while reducing MPG)  

I have had three dodge trucks all setup in excess of 7000lbs each the first when I got it was recieving 5 mpg hwy simple ignition upgrade improved the fuel economy by making it run more efficient while still using 87 octane up to about 8mpg's with 4.10 gears and non lockup tqflt 727a.  the second was setup for better highway economy it had 3.28 gears (stock had 3.90 gears) this dropped the rpm while running down highway boosting fuel economy.  And notice I did't go as drastic as 2.83:1 which actually does bog down the engine getting it moving.but remember dodge trucks are extremely torquey I have broken three np241 transfer cases. third one has a good city setup with 3.90 gears... for these examples gear ratios have severly affect fuel mileage. as well as increasing the ignition efficiencyaided in changing fuel efficiencies all modifications were done one at a time to prove effectiveness of modification.  

I do know that dodge had vaccuum disconnects on 1983,1987,and 1989 dodge w-series trucks.  I have owned all three of the above listed years with spicer 44f front axles as well as rear axle models of chrysler 9.25, spicer 60, and spicer/dana 70.  I do have a complete driveline you could see if you need pictures of pre 1990 dodgetruck with spicer44f front axle with disconnects.  

dodgethis:
I have had three dodge trucks all setup in excess of 7000lbs each the first when I got it was recieving 5 mpg hwy simple ignition upgrade improved the fuel economy by making it run more efficient while still using 87 octane up to about 8mpg's with 4.10 gears and non lockup tqflt 727a.  the second was setup for better highway economy it had 3.28 gears (stock had 3.90 gears) this dropped the rpm while running down highway boosting fuel economy.  And notice I did't go as drastic as 2.83:1 which actually does bog down the engine getting it moving.but remember dodge trucks are extremely torquey I have broken three np241 transfer cases. third one has a good city setup with 3.90 gears... for these examples gear ratios have severly affect fuel mileage. as well as increasing the ignition efficiencyaided in changing fuel efficiencies all modifications were done one at a time to prove effectiveness of modification.

I have had several GM trucks 6K and more and none got below 10 MPG even towing and all had 3.73 or deeper gears. I still own a 70 J20 that I drove cross country once in 94 and it averaged about 15 MPG. When i used to tow a horse trailer it would do about 11 or so. I also have a 89 4x4 burb that I bought new that is still pretty cherry and has 180K miles on it and it will do about 18 MPG all day under 70 MPH and it is stock (no duals, aftermarket ignition, air cleaner, big tires or such) expect for advanced timing and high octane fuel. My stock 2000 K3500 averages about 9 to 10 mpg on road with 4 studded bias plied 10 ply traction grip tires that do not roll well and a heavy Fisher snow plow and salt and spreader averaging about 8500 to 9000 lbs GVW. If I drive it in town and plow a lot it drops to about 7 to 8. ( track all my expenses) Empty it weighs about 6k and in street tires it does about 13 in town/rural and 16 or so on road. (all on 89 octane or better fuel). Everyone that I "know" with a dodge drinks gas like it has a hole in the tank at times. BTW, I remember driving some 93 to 94 Dodges when new with CTD's in them and they all had lockout hubs. Starting in 95 they had disconnector. They must of had a few different configurations.  

Still haven't got to O2 sensor or exhaust. With warm weather the fleet order changed around so desperate need of mpg's went to back burner. The bed self destructed and with whatever bed it gets(I'm eyeing an old Ford bed for about $50. Drills and sawzall's are great)I'll do exhaust n O2 while everything is opened up. No disconnect on front axel,and I know all 4 spin when beat upon(deep ruts but lots of fun,I was going to redo that driveway anyway). Go to Jeeps n hear about next crazy bit of fun. Wrench Wreck Repeat  

Duals are not going to help MPG like you think so save your money. Your best bet is to get hubs for front axle in 2wd and use smooth treaded narrow tires at near max pressure and find a way to advance timing and use better fuel is you best bet here to improve MPG. Anything else is kinda wasted effort. Dodge did not have a active knock control system that year and used retarded timing to tolerate 87 octane fuel which can kill MPG.  

get the o2 sensors. it will help a lot with the fuel mileage issue. not positve but your truck might have a dana 60 front. don't quote me on it though. a set of lock out hubs will help with fuel mileage also. some long tube headers with a nice exhaust will help. it can't be too big though. a single inlet muffler with dual out let is your best bet. an msd ignition system will help but they are expensive.