Here is a list from Manwithoutaplan on why the 6 inch lift is crap. Here it goes
1. If you are 4x4 you have to cut a cross member to fit the drive shaft.
2. You do not gain any travel from stock.
3. You diff hang lower than the front member.
4. The Pro comp shocks are stiff as hell including the block.
5. You get shit constantly for having db lift.
1 cv joints are level if you are 4x4
2. Spindle is stronger than Stock.
3. With 35's you have to do some form of triming