Are your gears stock? If so look for the axle code either on the tag in the engine bay or in the door jamp. It's usually on the last or one of the last lines and will start with a g, like g382. Either post up the code here and I'll tell you what it is or go to toysport.com and check their chart. If your truck is the one in the avatar and is 4cyl with manual tranny it's most likely 4.10.