I agree with Bill-E that you need to do the suspension first. I recommend KYB Monomax shocks all around. Upgraded the front bushings to the '03 & later to the OEM poly bushings, then add the Explorer Express rear anti-sway bar or Roadmaster Active Suspension to the leaf springs. After that do the intake, then the exhaust (most people here have gone with a Flowmaster that suites their sound requirements), and definately do the SCT XCalibrator 2 in order to reprogram your engines computer chip for better performance.