2003 Oldsmobile Aurora loss of power/acceleration

I have tried everything I have been told and my trouble still persists. My 2003 aurora has gradually started to lose power after I got my a/c fixed. Prior to that, it felt sluggish and I took it to the dealership. They say they discovered a crack in the intake and fixed it. After that, the car felt like new. My power had come back and I barely skim the gas and car pulled strong. But because of the heat, I got my a/c fixed, and gradually, the power started to fade to the point where uphill, the car decelerate and I have to press the gas hard so it could go, Changed the fuel filter about 4 month ago along w/ putting new spark plug( all 8). Coil pack front/back failed last year 's been changed. New air filter put.. Lastly I have clean my MAF and I noticed a slight increase when accelerating from a stop but only when the a/c is not running. I got a little more power when the a/c ain't running but I used to have power w/ a/c on when the a/c just got fixed for about a week before the power start decreasing.