Sorry, I don't fully understand when these shims are necessary? Can someone explain them. Example, I install the TM 4inch lift and have vibrations, will shims fix it or just a 1 piece drive shaft? I heard shims are only necessary when using blocks or shackles for large amounts of lift, and that if installing a new entire leaf pack you wouldn't need them. (considering the lift is equal). Thanks in advance.

shims are used to make the driveshaft ujoints angle equal. they may or may not be needed with all suspension lift types.

here is a good tech page on how it should be setup. (read the stuff on the right, too)
http://www.4x4wire.com/tech/pinionangle/

Thank You! That was exactly what I was looking for. Explained perfectly.