Wow, so much bad information in here. Not everything posted is wrong but a lot of it is or is misleading. No offense to anyone, there's a lot of confusion and myths out there about the CUCV's.
I just sold my M1008 on 38's.
Bone stock with the 31's they're slow and noisy. Put OD in and/or taller tires and they're slowish to okay and noisy. I went the big tires route and it got quieter at speed and wasn't bad.
With 3.73's you should be able to spin 33's or 35's all day long at a happy cruising speed. Bone stock with 4.56's and 31's they went about 55mph and it sounded like the engine wanted to come through the firewall and beat you to death.
They're bare bones, ride like a 1 ton (but not as bad as the 1 ton IFS trucks in my opinion), and large and old. Maintenance might have been excellent or all kinds of redneck sketchy. Some units took excellent care of them while others didn't at all. You definitely need to look one over before buying it.
They're all GM parts bin stuff. Nothing special.
-M1008 is J code 6.2L, TH400, NP208, and open D60 and Detroit Locker 14FF with 4.56's in both.
-M1009 is J code 6.2L, TH400, NP208, and 28 spline 10 bolts with 3.08 gears, open in the front and Gov-Bomb in the rear.
-M1028's got a Dana limited slip in the front and depending on the model a NP205. The M1028A3 dually got the Dana 70 rear axle.
The weight ratings are just a function of the military actually rating them at their rated capacity and not the GM "sales number". Everyone sells a 1 ton even today but do you really think a '11 C3500 Silverado with a Duramax can haul the same ton as a '69 C30 ?
Pretty much just order all the spring beefing options you could in the '84 era and you'd get the same springs the trucks go. The M1028's just got the even heavier but still parts bin severe duty springs that were mostly commercial only applications.
Uhm...find one in decent shape and well running and you'll be well served. A member on here did what you suggest and swapped his 3/4 ton axles under his M1008 and used it as a daily driver on 35's. I believe his 3/4 ton axles were 4.10's though.
Oh, and the 6.2L is no slower than a carbed small block of the smog era. They were designed to compete with that only getting a lot better gas mileage. As far as the mileage goes...in a K5 with 3.08 gears, stock sized tires (probably 29" 235/75R15's), and a 700R4 they've been reported up around 30 on the freeway. A M1008 with no OD, 4.56's, heavy everything and big tires? Forget it. 15mpg max. I was getting 13mpg but I was spinning heavy ass Michelin 38" tires with an otherwise stock truck.
That said a similar civilian truck with a gasser would be getting 13mpg if it was lucky. 10 if it was a BBC and god smiled upon it.
