I have owned both a 2004 and 2012 5.3 with not one bit of trouble out of either. My 2004 was running great when I traded it last year, and got a great trade in on it. Just wanted to upgrade to a crew cab with 4X4.
It was well worth the money. The kit came with extra pieces so that it would fit the WT, LT and LTZ models which are slightly different. I finished installing all pieces in about 2 hours, and all parts lined up perfectly. On a scale of 1 to 10 with 10 being the easiest. I would rate the install an 8!