I own an 84 chevy shortbox, it has a built 383, an 700r4, 12 bolt rear and 10 bolt front axle, a 4 inch lift, and 33/12.5/15.
my problem is that i shift all of my gears before, i reach even 20 mph. when i hit the highway, my truck is screamming to go 55, i just recently bought the truck and it's my daily driver, what do i need to do to be able to cruise 75 mph, i believe the rear end have been changed but i'm not certain, i know the speedo is way off, because when i'm going between 40, 45, my speedo says im going 65, 70 any feed back will be helpful  

Sounds like you got yourself a tractor. find out what size ring and pinion u got.  

Not to make fun or joke but is the t-case in 4LO?  

No it's not in 4lo. but it does have full time front hubs, so how much would putting part-time hubs make a difference?  

saltiej:
No it's not in 4lo. but it does have full time front hubs, so how much would putting part-time hubs make a difference?

No difference at all in engine RPM  

but it would make a difference in the amount of drag on my truck? i would think that the level of resistance, from constantly pushing my front axle and driveline. i would think by freeing up my front wheels, would make some difference.  

if it is a part time tcase, yes, if it is a full time case , no because it will not move unless you lock it.  

i have a np208 transfer case which i'm positive it is a part-time transfer case.  

A 208 is part time, Lockout hubs would help.  

how much difference?  

Maybe 5 to 10% on MPG. THe higher amount if you have a stock truck the rolls easy, the lower amount if you have a lifted truck with a lot of drag.  

Your probel sounds like too low of a gear ratio in the diffs. pop the cover and see what the ratio is. 456s or lower are not so good for the highway.  

Your problem sounds like too low of a gear ratio in the diffs. pop the cover and see what the ratio is. 456s or lower are not so good for the highway.  

rumblebee4:
Your problem sounds like too low of a gear ratio in the diffs. pop the cover and see what the ratio is. 456s or lower are not so good for the highway.

4.56's are fine on highway with a OD tranny and if you have big tires, even a 4.56 is not enough with a OD tranny 35's and larger tires sizes.