GMC/Chevy are the same, twins, at least mechanically. GM uses the 4.8L/4-spd combo in some 2500 and 3500 vans. Make sure you get the 6.0L/6-spd. 3.42 is fine and the highest numerically offered. The 6-spd trans really helps. You'll have 5 usable towing gears vs. 3 of 4-spds. smalelr spacing and way shorter first gear to get you going and into the 6.0L peak torque over 3000rpm quickly.
Compare the ratios and torque multiplication in column E:
You should be good for up to about 8000 pound dry TT with that combo. You may need a replacement receiver.
