so a little background first, my truck is a 94 4x4 5 speed w56 22re w/ 225/75r15s that gets about 22-23 hwy mpg doing about 55-60 at about 2500-3000rpm. Is it possible to swap out the fifth gear from a w58 (or to swap the 1st 2nd and 3rd gears into a w58 as well as the transfer case), essentially making my truck stay in the 2500-3000 rpm range at a higher mph?

 

Are you planning on going to bigger tires? If so then most people rehear their differential. I know a few other people have asked about swapping transmission gears and such but I don't think much comes from it.

If you just planning on going to to 31's then finding used 4:56's that you can unbolt and swap in to you housings isn't that hard and it's usually fairly cost affordable. 4:56 seems to take you back real close to stock with 31's

 

im searching this same thing right now! according to a marlin forum, as long as you use the bell housing, output shaft and rear section/housing off of the 4x4 donor transmission it can be put on the w58. It should bolt right up but I'm trying to find someone who has done it first before I do it. Im running unimog axles with 7.56 axle gearing that can NOT be changed. My top speed right now is like 45 at 3000 RPMs. Going to 40" tire and a w58 swap will put me at some decent highway speeds, in the 60's depending on how high I want to take the rpm's.