car has been running great for years all at once last week I got a massive power drop off. car still starts, runs, idles perfect just its like I'm only getting half throttle.

I change 2 fuel filters and cleaned the k&n air filter. also I installed a boost gauge to see whats going on with that. showing 9 psi at full throttle 3000 rpm. I think it should show 12? car idles and runs very smooth just takes forever to accelerate. like half or so throttle.

anyone have any advice on where to start diagnosing? also is there a way to do a compression test?

thanks as always for any help guys!!

you guys have been a HUGE help in my travels with these cars