wow, just stumbled across this. where to begin......i will do my best not to sound like a dick.
how/why are you modded if you dont know anything about the car?
any FI car will lose power as mod levels increase w/o a tune. (minor things like sri's dont really apply). but based on your lack of knowledge (no offense) you need to do a lot of reading before you do anything else. do you have a Dashhawk or the like to monitor engine vitals?
I would suggest the AP, i love mine, but expect to pay about 500 bucks on top of the cost of the AP for a custom tune. I would stay away from ATR since you really dont know what your doing and can very easily blow a piston through the side of the block.
also, since you have a speed6 i would recommend the rear diff mounts first