I have a '98 12v auto. with an AFE Stage II air filter, #5 TST plate, moved forward, and straight piped factory 3" exhaust. A friend of mine has a '97 12v 5 speed completely stock except for straight piped 4" exhaust. The odd thing is that his truck sounds louder and throatier (is that a word?) than mine. I think it's because he has 4" exhaust instead of 3". Any opinions?