sorta new guy

[brother rat]

Hi there. I'm currently driving a 2004 Sport Trac 2WD. It runs great, and I really like the vehicle. It is getting older, but only has about 130k miles.
The 4.0 SOHC has been a great motor, so far, if not slightly underpowered. Any recommendations on getting even a little more juice out of it? Bolt-ons? Tune?
Any reasonable bolt-on exhaust available that doesn't sound horrible? I'm in SoCal so the catalytic converters will remain in place.
I will probably end up replacing the rear end gears with a different ratio and maybe a torsen style diff. Recommendations there? Experience?
The foam in the seats is starting to disintegrate and the upholstery is wearing thin. Replacements? Seats from newer vehicles fit easily?
The only real issue I have right now is that after driving, in Park, the idle runs up to about 2500. No CEL. I'm thinking maybe just a dirty sensor somewhere. Is this a known issue?
I'm trying to think through what to do with the bed, or how to best utilize it. I have a small toolbox back there right now. I don't have the factory extender or cover. I've considered a camper shell and carpeting the bed. What have you guys found to be most useful and for what activities?
Thanks! I know some of these have been answered before. I've looked through a lot of threads. Being that the vehicle is old enough to have its own driver's license a lot of the info in those threads is outdated.

 

[JohnnyO]

I had two Sport Tracs and only traded my last one on a new Ranger a few months ago.
There aren't many speed parts left any more. Zabtek quit making the bored out throttle bodies I think.
Best bang for the buck is a cat-back exhaust. I had a Gibson exhaust on my '08, it sounded good and picked up a few hp, Gibson says 8.
Yank the silencer out of the intake tube and get a K&N replacement filter.
Torrie at Unleashed Tuning makes a tune that the Sport Trac guys like. I didn't use it myself. Cost is about $450.
Torsen is the best diff. A Detroit True Trac is the same thing and probably costs less. You have a 31 spline 8.8" rear.
Seats, check with an upholstery shop. Best bet is probably a better set out of a junkyard.
I have no idea what would cause your high idle speed. Could be lots of things.
Used extenders turn up here and there. I don't think any of the cap manufacturers make them for Sport Tracs any more. I kept mine when I traded it in and sold it locally for $350. I used a vinyl roll-up tonneau in the summer and the cap in the winter. The tonneau companies might still make them. Try Lund or Truxedo.

You can also look at www.sporttrac.org and there are Sport Trac forums at www.explorerforum.com.