[Ski-me]

I'd recomend Steel Shims that bolt to the spring pack. Not the aluminum ones. Aluminum tends to get brittle and can break apart...not good. And the aluminum ones I've seen don't bolt to spring pack (pro-comp comes to mind). Just be aware.

Also, with a 4" lift, you may end up with driveline vibration issues. Really depends on truck. But more likely, than not. As a short term fix, you could drop your t-case with a t-case drop kit. Don't use the small, think washer stack you may currently have that is on top of the t-case cross member. They are not strong enough to use as a drop spacer.

Once that is done, your t-case angle should be parallel with your axle yoke angle. That's with the stock driveshaft. With the lift and tcase drop, your driveshaft is also going to be too short so you may have to lengthen it too. Just have to see once installed.