i ran 1.5" spacers on the back of my 2500hd and towed my toy haulers about 11-12k lbs no problems. my buddy has them on all 4 corners of his monster ford, tows a bumper pull same weight, no problems. 2 other buddies with duallys , 37's, on 22.5's, tow monster 5th wheel toy haulers, no problems. i was nervous at first from what i've heard, but none of us have had any problems at all.
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'05, gauges, banks bullet, st. pipe, silencer ring mia, bags, 50 gal aux tank, 5th hitch, air box modded, 8" lift, 20 RBP's on 35 toyos