56GMC, Like John wrote,you can change the gears in your diff w/o changing out the whole rear end.If you don't ever need to start out in 1st you've got a "granny" gear in there.The way I found out my rear end ratio was to raise up the back of the truck on jack stands, put a mark on the drive shaft,and another on a rear tire.Then,with the tranny in neutral,turn the driveshaft by hand while watching the chalk mark on the tire.Count how many times your driveshaft turns once you complete one full turn of the tire.That is your rear end ratio.Example:Drveshaft makes 3 1/2 revolutions once the mark on the tire has returned to original position.Rear end ratio= 3:55.When you do this make sure you chock the front wheels so the truck won't roll off the jackstands. God bless,Frank
'69 Chevy C-20
292 3spd.
