My car is a GT 2

My car is a GT 2.7L 6-speed and it doesn't feel like its pushing full horsepower. Also, when it reaches normal temp it idles a bit rough. Like a slight shudder you can see looking at the engine and feel sitting in it. But the rpms don't move. When driving, I take my foot off the gas to coast and when I depress the gas again (not flooring it :) ) the car jolts. It feels like when you catch a gear hard when shifting. There is no check engine light and no codes.
What I've done so far: new plugs (ngk iridiums), wires, TPS, fuel filter, air intake hose, air filter, cleaned the throttle body, MAF sensor, and IAC valve. I went to Valvoline and had the full fuel system cleaning and just got an oil change. This is driving me crazy! Any help is incredibly appreciated.