Degree shims for 3" lift?

So I snapped off half of one shim, and lost another completely on my first wheeling trip with my 3" lift (full rear leafs). Well I called RC up and they mailed me some new shims no problem. I put them on today...and I couldn't help but notice they seem to be twice the size of my original shims, and they tilt the axle forward a bit.

It made me wonder, what's typically the proper angled shim to use with a 3" lift? What about a 3" lift with 1-2" lift shackles?

Also, what should I look for on the axle for the proper angle?

I think the shims I got were something like a 6-8degree shim (about twice the size of the original shims if I remember correctly from eyeing it).

6 to 8 is a big difference, 2 degrees to be exact.
The best thing you can do is get an angle finder for $9 from HomeDepot and order STEEL shims that will work with your measurements. You want to be within 2 degrees, 1 is prime.
Where the shims aluminum?

They look aluminum, so I'd say so. Unless grimus wants to chime in, we'll never know.

But how do I find out what degree I want, what am I looking for?

Take that angle finder (some of them have a magnet on the bottom) and stick it to your drive shaft. Take that measurement. Then measure the pinion. There are a few ways to do this but I like to use the angle finder along the diff plate bolts (or a flat surface in that area and figure the measurement from the nearest 90*) to find that measurement. The difference should be within 1*. Whatever difference you get should tell you what degree shim to use.
It may sound complicated but it's just the difference between the pinion and the driveshaft angles.
Aluminum shims have a market for some odd reason, for us, steel is what you want.
Summit may have them, if not, RE does.