1971 gmc gear bound!!

[ookla]

Im trying to get better top end speed and gas mileage out of my 1971 K2500 gmc-canada made truck. It has a pto dump bed (dealer aftermarket-I think)as well as being 4wd, so I thought it would be easier to change the differential gears instead of changing out the gearbound 4spd and transfer case that's in it (and not sure a higher geared set would be right speed for my dump setup). Im having trouble figuring out which gears are in it. I believe the front is a dana 44 and the rear is a dana 60 -10 bolt styles. markings are : front:
C81256 and 44 5F on differential housing, and rear: C80255 and 60 on differential housing. I think I could get different gears for front and rear--say 373...? but don't know how to figure out if that will work or not??? anyone have any input? thanks

[Hawghauler]

I would be looking at more gears in the tranny. It'll cost about the same as new gears, but will leave you more bottom end grunt. Overdrive makes it much more street friendly, while bottom gears sometimes even improve the hauling/offroading capabilities.

[seattle gmc]

Im considering going with a gear vendors overdrive unit, when i get to that point on my K2500 with four speed. Since the gear vendor units are so expensive i might hold off for a while, but i think that is what i will use to make the truck more driver freindly at highway speeds. I also want to keep the truck as original looking as possible, with little to no mods, or i would consider going with the ranger gear splitter set up.

[hugger6933]

A NV4500 may be the best and cheapest conversion out there for you. The ranger gear splitter and the gear Vendors overdrive are gonna be pricey. The newer G/V setups are a bullet proof proven on the track in cars like pro mod up to like 2500 hp so I think it would survive in a 4x4. Check into their websites I think their splitter will give you more than one OD. Meaning you can have better gas mileage than first thought. Jim

[ookla]

Hawg, got a granny in the tranny...no need for grunting. I drive it to and from work, so no offroading nor much hauling beig done either, just wondered how hard it would be to find higher gears for the differentials and how benificial it would be. Not sure I wanna mess with rebuilding the insides of a tranny, but it may be easier than im making it out to be, or the diff. gears could be less benificial than I am hoping for....dunno

[oldchevynut]

ookla, Welcome to the site from another Kennerdell,Pa newbie. Randy.