Rear End Gear ratio
If my memory serves me correct, the ratio is based on how many rotations the driveshaft makes for one complete rotation of the tire. I belive the gear ratios available for Chevy trucks (14 bolts for the rear cover on the differential) would be 3.42, 3.73, 4.10, 4.56, 4.88, and 5.13.
If you place the rear of your motorhome on jackstands, block the front tires, and place the transmission in neutral with the emergency brake off, you should be able to rotate the rear tires. Now make a mark on the driveshaft where it enters the differential and on the differential so they line up. (a peice of white tape on each marked with a black line works well) Now place a block of wood next to the rear tire you are going to rotate (this is to get your reference mark close to the tire) with the marks lined up on the driveshaft and differential, make a mark on the tire and the block of wood. You will now rotate your tire one complete turn while counting the number of rotations of the drive shaft. A little less then 3 1/2 turns equals 3.42 ratio, 3 3/4 = 3.73, a little over 4 turns = 4.10 etc.
Don't forget to account for any change in tire diameter for your speedometer drive. Hope this helps. "Mac"