I bought my 2008 GMC Sierra Denali used, I opted to get the 3 year 36000 mile warranty they were offering me. I wanted to get aftermarket exhaust installed on the truck, which would cost me 200 bucks at the local muffler shop. Well the dealership where I got the truck is trying to tell me that if I install the aftermarket exhaust, it will void my warranty, but we can do the same thing for 1000 bucks and its not going to void the warranty. So I guess my question is are they just trying to get 1000 bucks out of me, or will it really void my warranty?