Mitsubishi Repair: 3000GT power loss at 5000rpm, cold air intake, engine tone

Question
I have a 95 3000GT n/a, fwd, mt. As of this morning, it seems lil sluggish while driving and when I get the rpm's over 5000 it loses all go-go power. Like someone is holding back  the engine, the engine tone changes too, like someone is plugging the  exhaust or air intake, muffled sounding. Brand new exhaust, no CAT, and K&N cold air intake, both have been on the car and running fine for last 4 months+. Car sounds lil rough while idling too. I pulled both banks of plugs and they look fine. Pulled plug wires off one at a  time while running and all are firing. Any suggestions would be awesome, mechanically inclined but mostly a customizer so  at a loss here. Thanks James

Answer
Veryify good idle vacuum (over 19 inches at idle) if low, find mechanical cause such as jumped timing.

I would check fuel pressure and exhaust backpressure when the vehicle looses power. If they are normal (fuel pressure at spec and exhaust backpressure low, then I would look at the MAF sensor, as it controls fuel injector volume to the cylinders.