Looking for good advice from performance gurus on TDR. My truck is an '01 H.O. 6 speed that has one of those old Dyno Sources Power Buttons set at 30 and a K&N air filter; other than that its stock. There's 165,000 miles on the truck. Fuel pressure is at 8 PSI on idle so I have a FASS 95 GPH pump on order to fix that situation. But on the performance side, I have decided to use Formula 1 Diesel's Mach 1.6 Fuel Injectors. I don't want to go over 500 hp with my Power Button activated. But, my question though is really about moving air: once I install the injectors, will it be advisable to move to a 4 inch exhaust, even though the turbo and downpipe remain stock? Thanks in advance for any advice!