Chock one rear wheel, or stack up some boards under the tire so there's a little weight bearing on it. That will assure there's no movement as you watch the other wheel turn. A 4.10 rear end gear, which your rig probably has, will take slightly more than two turns of the driveshaft to make a single rear wheel do a full turn. The spider gears double the speed of the rear wheel if only one is turning.
That's something to remember with a vehicle that's stuck in mud or snow- - - -if a single wheel is spinning, it's moving twice the speed that the speedometer is indicating.
Jerry
