also I put this in another thread a couple minutes ago. use Shell Vpower. they use this additive that is required by Law to be in every gas. they usse 5 times more of it than the law requires and about 3 times more than any other gas in the US here is some info from shell's site
"On today’s tough, demanding roads, performance is what counts. At Shell, we believe all great performances begin with a clean engine. Shell V-Power® premium gasoline can clean up deposits on intake valves and fuel injectors left behind by low detergent gasolines. That’s because it contains more than five times the amount of cleaning agents required by government standards. Shell V-Power is also recommended for vehicles that can benefit from higher octane (check your owner's manual for the octane level recommended for your vehicle.) Try Shell V-Power. It actively cleans for better performance."
a cleaner engine means more miles per gallon and more horsies. so although V-power is a bit expensive and not something you could afford all the time. use it every so often and itl improve your fuel economy.
also get all your oil replaced with castrol syntec.