I get about 12 all-city with the mods in my sig and I drive like you do big. I have 4.10's ... What I'm wondering though, you didn't say he has an intake, that could be part of it too...? Could even be tire pressure maybe, even front end alignment, I wanna say since he may not be the kinda guy to check that stuff as often as he should considering the banks junkie he seems to be
But I won't. LOL!