If your looking for bolt ons. You could go with smaller tires effectively lowering your gear ratio. Since it's 2wd, if you lower it, it won't look funny either. 235/40/17 are 24.5" tall. 235/45S ARE 25.5". Both look fine on a lowered truck. Just get some used 95+ Mustang Gt rims. They fit perfectly and are usually cheap. The ones I have weigh only 16 pounds each.
Lowering the truck will improve aerodynamics a little too.
Other bolt ons for a little more grunt would be a complete 2.5" exhaust with new cat. Just get a generic cat and Dynomax muffler from Summit and take it to a local shop for install and pipe. About $200 depending on the shop. Want a little more torque? Headers... $300 and up last I checked.
Mustang MAF, and throttle body mod. Will help at WOT, but won't hurt fuel economy unless you keep your foot in it all the time. K&N replacement or cone will allow more air to get in too.
A 410 cam is considered bolt on.
change your O2 sensor. Everybody overlooks this. they are only 60K mile part. Switch to synthetic everything. Especially tranny. A good tune up will go along way. But depending on your mileage, you may need a rebuild, or new heads. I recommend a compression check.
One more bolt on to consider is kinda spendy, supercharger. They have them for the second gen, but I don't see why you can't put it on the first gen.
I don't know what gearing you have, but I have a perfectly good 3.73 you can have for shipping cost.