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.