I've seen all the front leveling kits but I was wondering if someone has leveled their truck by lowering the rear. I was curious if you have to change the pinion angle too. Ive seen the shackles, but haven't seen what a truck looks like with them. I have a '06 F150 too.

 

Several members have. Try looking in the 2004-present forums. I think one of the companies includes new shims with their lowering shackles.

 

I lowered mine in the rear. I had to run the shims to change the angle... It vibrated so bad I couldn't even drive it. But I have a two piece drive shaft and I know some just have a solid drive shaft. If you do then you can get away with not running them.