i have been browsing around, looking for a decent exhast for my gas '04 6.0L 2500HD crew cab GMC to help boost my mpg. i do tow a car hauler on the weekends during racing season so im still going to need some decent torque, yet it is also my daily driver. im going to get a CAI soon to help out with flow but figure if you are going to get the air in, you need to get it out and everyone knows the intake cycle begins with the exhaust. i would like to put in headers on back. would i see the most gain in just replacing the manifolds with headers, or would i have to replace everything.

i have asked some people about this and got different responses from "the mufflers are the most restriction" to "replace it all". i am not concerned with sound at all (just dont want to wake the neighbors) as no mater what you do, it still sounds like a stock cam.

what are the sizes i should be looking for, and is there anything else i should be aware of.

 

i have a 03 chevy 2500hd 4x4 with the 6.0l ext cab short bed. the truck has a flowmaster exhaust and a cold air intake. i think your biggest gain will be with the muffler and headers if you want. the exhaust design is actually pretty good by chevy. no y pipe, dual pipes with dual cats from the manifolds with a nice size pipe. like you said you dont want to loose torque so choosing your muffler will be the decision i would stay away from the totally open ones like glasspacks. and headers will also be good but like the saying goes high performance means high maintaince, youll be tightening thoose babys up every weekend. as for mpg i get about 12 around town and 14-15 on the highway depending on how fast im driving. the 4.10s just kill me on the highway.