I had fittment issues with my tsp headers and y pipe, i have a 2006 Sierra z71 with the 5.3, the headers and y pipe were supposed to be a direct fit. I left the header bolts loose while attaching the y pipe, all was looking well. Once I tightened the header bolts the headers were making slight contact with both the driver and passenger side on the frame, and the crossover from the driver side to the passenger side was slightly rubbing the drive shaft, I loosened the bolts and tried some different things with no resolve. I spent about 5 hours working on it to get the clearance needed but ended up having to heat and make small indentions with a pry bar to keep them from making contact. I checked my motor mounts and transmission mount for slack or play and they seemed tight and looked good. They did bolt up to my factory cat back like it was supposed to. I was kind of disappointed because the headers and pipes were well put together and look to be good quality just didn’t fit like I had hoped. I would have sent them back and tried a different set but instead of dropping the cross member to remove the factory y pipe I cut it out after I had mocked up the headers. I needed the truck because it’s my DD so I had to make due with what I had, the clamps provided did leak like others have stated but I put some copper silicone on the pipes and slid them in then added some to the seams and put the clamps over that.