having some issues, just over 100k miles and car is becoming more sluggish. Sometimes it will surge while taking off and accelerating but idles and cruises just fine. I turn the car off and back on and 99% of the time it's fine. When it does this the trans shifts hard. I don't do a lot of hard driving but sometimes I want to take off and it revs a lot and puts out a little like it's "tired". No engine light but lately it idles a little rough. Mechanic says it's fine and they can never reproduce but it's annoying when I'm running late or have friends and have to stop and restart the car. It also starts up hard like the engine isn't mounted down enough sometimes and it might shake when I shut it off. Usually I never feel the engine even when starting and stopping. One more detail the temp gauge usually rests under half way. Is it normal for it to go slightly past 3/4 before cooling down? I know that's a lot but want to be thorough. 2005 Grand Prix GT 3.8 V6 normal aspiration, no supercharger
