The best, easiest and most accurate way to check rear gear ratios is to jack the truck up. With both tires just clearing the ground, put a piece of tape on the inside of both tires. Put a piece of tape on the ground next to each of the tire tapes. Put a piece of tape somewhere on the driveshaft or yoke so that it hangs straight down and is easy to see. Get a helper on the other tire and turn both tires in the same direction, at the same time. Count the number of turns on the drive shaft, until the tires are back to the tape marks and have made one revolution. If you should happen to have posi, both tires will turn together in the same direction. If the drive shaft turns past 3 turns and ends up on top, it has 3.50:1 gears. If it turns just shy of 4 turns it has 3.90 gears, or just past 4 turns, it's 4.11
