1) Do not stack additional shims on top of existing shims. Buy 6 degree shims.
2) Heed Jon G's warning about securing the new shims in place. Since they are tapered, they will walk out of position if not secured.
3) Using 6 degree shims in the truck with power steering is not equal to trying to out-think GM engineers. Adding power steering to these trucks already changes the engineering.
With two degrees of castor with power steering, the wheels will not come back to the straight ahead position after coming out of a turn like a stock manual steering box does.
Six degree shims will correct that, as well as give you much better feel of the road. The truck will naturally tend to go in the straight ahead position while driving.
