I'm looking to buy a catback exhaust...i do alot of town driving now but am also on the interstate for a few miles...my truck only gets about 10 in town so i was hoping that with a catback system i can increase that by a couple..with that said i want a system with the following

1. best increase in mpg
2. deep loud tone at idle
3. no drone at cruising speed
4. loud at high rpm
5. not horribly expensive
6. would like 2 tips somewhere whether it's si/do or 2 si/so..

thanx...wes

btw...i have a 98 f-150 with a 5.4 motor