Rear end calculator (your truck's, not yours)

[jfalesi]

For reference, a 3.73 rear end is assumed. In 3rd gear (or direct drive), at 50mph your engine rpms will be 2000. To calculate your actual rear end ratio, check your rpms at 50 mph (only works in 3rd/direct drive gear). Divide your rpms by 2000 and multiply by 3.73. For example, if your rpms at 50mph are ~ 1850, you have a 3.42 rear end (1850/2000 = 0.92, 0.92 * 3.73 = 3.42).