k i have a 2001 full cab 4x4 trd w/ 3.4L v6, and it has about 185,000 miles on it. i havent had major problems with it at all, but i can tell it has lost power, gas mileage, and im starting to have minor problems with it. I'm thinking about getting a K&N FIPK, a flowmaster muffler, and maybe a throttle body spacer. How will these affect my truck? in a good or bad way? i would also like to know any tricks or upgrades that can make my truck run a bit more like brand new. Thx much

None of those will improve your truck, all it will do is lighten your wallet. A smart thing to do is to use synthetic fluids throughout such as oil, tranny, etc. You talk of minor problems you're having, care to enlighten us? If you haven't done so already, you can do the deckplate mod to get a little more kick in the pants feel.

Putting all the other stuff on it is just covering up the original problems. You need to figure out why it's lost power.

Assuming you got all the normal PM stuff done recommended in the service manual.

The easy and most telling check is a compression test. If the compression is low, then your valves and/or rings are showing their age. Then check spark. You might need new plug wires. I am assuming the plugs have been changed. The O2 sensor and airflow sensor might also be old. Check the timing too. A good throttle body/intake cleaning never hurts. Fuel pump might be getting old and loosing pressure.
If all the above checks out then get the fuel injectors cleaned. The stuff in the bottle does not work. A shop like http://www.rceng.com/ will clean them and bench test them for about $25 bucks each.

After you have done all that, it should run as new and be good for many more miles.

i beat the bushes about the deckplate mod, and ive been hearing that its almost the same as getting a K&N FIPK gen II. if you have the cap out w/ the deckplate mod, wouldnt it just be sucking in the hot air from the engine and everything?

Then do the elbow mod instead if you're concerned about sucking in hot air, but you really don't have anything to worry about IMO.

http://4runners.org/writeups/airbox/index.html

i get the regular checks, oil changes and everything. do they usually check all of the above when they do the basics? if not, is it easy for me to check myself? im new to this type of thing and i dont want to screw up. thx much