The best way to do it would have been using an "angle protractor" - one of those magnetic deals that you can slap on your 3rd. The triangulate the geometry of the truck before and after the lift.
Not good at geometry? The rule of thumb that I used for my front axle end rotation was 1.5 inches of rotation per every inch of lift. The front has a shorter driveline, so 1.5 inches might be too much for the rear. I'd go with 1 - 1.25
Other things to consider: Did you change shackles? If you shackle up the rear - as most rear spring swaps do (esp the Chevy's) - this helps rotate your pinion.
On my truck, with the shackles, I used a 3 degree shim...
Not good at geometry? The rule of thumb that I used for my front axle end rotation was 1.5 inches of rotation per every inch of lift. The front has a shorter driveline, so 1.5 inches might be too much for the rear. I'd go with 1 - 1.25
Other things to consider: Did you change shackles? If you shackle up the rear - as most rear spring swaps do (esp the Chevy's) - this helps rotate your pinion.
On my truck, with the shackles, I used a 3 degree shim...
