I installed my FIPK about 4 years ago with about 100k on the clock. I have a 2004 as well - TRD 4x4 with the 3.4 and auto. I noticed a pretty decent improvement around town in throttle response and acceleration, but it does get pretty loud when climbing a hill at highway speeds and the tranny downshifts. I wouldn't hesitate doing it again, though. I've had one on every vehicle I care about for the last 15-20ish years.