A tuner is not "needed" and you cannot change the gear ratios on the 96-98 cars with a tuner; you can only do that with a speed calibration gear, or something like that; can't remember the exact name. Edit: found it here:
http://www.americanmuscle.com/speed-calibrator-94-04.html. A mail order tune (which is what you'll get if you get a programmer from AM, which I would recommend because they do free tunes for life from Bama Custom tuning, which is a great deal) will probably net you 15ish horsepower and allow you to raise the rev limiter, which is necessary to rev the motor to its fullest potential with the PI stuff. Also, I'd be weary of a used tuner considering that you have a relatively decent amount of modifications to tune for. In other words, the tune that comes on a programmer for most cars will not best suit your car and the mods you have done on it. Unless you find a tuner that was used on a car very similar to yours with similar mods, I would get a new one. Once again, the AM SCT tuners are very tempting, considering that you would tell them all of your modifications, and then they (Bama Custom Tuning) would build a tune specifically for your car. The only thing better than this would be a dyno tune, of which you'd have to have the programmer anyway.
Do you have an offroad mid-pipe? I understand about not wanting/being able to do headers on account of cost and time, but an offroad mid-pipe is relatively cheap ($150ish brand new), very easy to install (3 hours with basic tools and never doing it before), and will net you a solid 15 hp and a nice sound.
That's not a bad deal for that package, although I don't know just how much hp you'll get from it. I can tell you that you won't get 28 hp like they advertise; maybe 15 at absolute best, and that's doubtful. But it will give you a better throttle response and room to improve other things in the future. I'm not real terribly sure about that plenum either; that doesn't mean it is bad or anything, just that I've never heard of it. Maybe some other members will chime in with some insight on this package deal.
If you are going to get both a tuner and this other stuff at some point anyway, I'd get the other stuff first. It's easier to install that other stuff while you are working on and have the motor torn apart than it is to reassemble the top end of the motor with the stock stuff, only to have to take it back off to put on this new stuff. The programmer would only take 5 minutes tops to put the tune on. Simply because of time and hassle saved, I say get the other stuff first.
