I know its probably on here somewhere but could somebody tell me the formula to figure out what gear ratio i have...thanks

 

Mark the tire and the drive shaft and count the rotations. If it goes 4 to 1 it's a 4.10. If it goes 3 3/4 to 1 it's a 3.73 and so on.

 

why not just check the label in the glove box for an RPO code? In the past, I've been able to take a VIN to a GM dealership and ask them to run it in their VIS (Vehicle Inquiry System) and give you a buildsheet. They can give you a run down of every single RPO on your truck. Your gear ratio will be on there, along with some other good stuff to know.