I have a 99' Silverado Z71 and my buddy has a 99' Sierra (Same truck w/different Badge) and it seems people are not happy with the Flowmaster systems.... I installed A Cat-back 20 series system on my truck and Couldn't be happier, I get hardly any noise inside the cab and it gave my truck an entirely new attitude. the system came with a resonator I will be adding another kit to the Sierra soon. The Kits come with everything you need to install, You most likely will have to replace the Cat bolts for they dont come off very nicely. -Jimmy