i went to the local exhaust shop and scored a deal on custom while they were doing my shocks. with all of my mods my mpg on the hwy is well over 20 and i would def have to say my hp is up. i was looking at the flowmaster kits and opted for the exhaust shop to go in and do their thing with the super 40 muffler and the tips of my choosing, that way it would be warrantied and fully welded.