It doesn't matter what the factory pinion angle was, it's what you need to be at after the modification. You have to match it to your transmission angle.
I don't know how to figure that out, but if you drop it further just take a measurement and you will find out then.
Well since I'm kind of new at this, I did some research on how to measure the angles, and that's what I did..then I read about what other people have done for this kit, and I decided that a 6* would be a good place to start. I measured the angles again once I put the shim in to make sure I got it where I need to be, and right now I'm within 1/2*. I got the shim kit from Summit racing, just search for a 6 degree pinion shim.
Hey everyone, new at the forum..Just got a 2014 Sierra a week ago and installed my Rough Country 2/4 Lowering kit on the weekend, took about 4 hours with 2 ppl. Love the look but there was some vibration. I got 6* pinion shim installed today and all vibrations are gone..