I have a 1993 Ford F 150. Am running 4.56 gears with 38in super swampers. I would like to know what I can do to get a lower crawl gear besides changing my gears in the diffs and what is the best up grade that I can do to the drive tran that doesn't cost an arm and a leg. and I have the 5 speed trany.  

you could run smaller tires for a lower crawl ratio, but i wouldn't recommend it. other than that, diff gears are  the cheapest alternative.

the best cheap drivetrain mod is a rear traction device. a lincoln locker(welded spider gears)being the cheapest. i don't know much about trucks but if your f-150 has a 9" rear like the older ones, you can pick up a spool pretty cheap. guys will argue both sides of having a spool on a DD but i would run it. you will have to sacrifice a little on road comfort for most off road mods. avoid the cheap lunchbox lockers, step up to a detroit if you're going to drop the cash on a locker. there are also some good limited slips on the market.

For the price of new gears f/r you might be able to get a gear reduction kit for your transfer case (if your t-case is gear driven) or get a different t-case all together (granted it probably won't be an atlas or marlin crawler).

Definitely go with a rear locker of some sort.  Whether it be a spool, a detroit, or a selectable locker.  38's with low gears will chew up any of the smaller lockers.

Scoutnut

I forgot to add that I already have a locker  

engine bolt ons are cool. and maybe a cam.