I've a 2006 G6 GT 3.5 coupe with 87600 miles and the past week the engine will rev up to about 3000 rpms shifting from 1st to 2nd when the car has either been sitting over night or all day in the parking lot at work. Once the engine is up to temp, the shifting is fine both up and down shifting. It's also very sluggish first thing. Almost like it doesnt want to get out of it's own way. I had the oil and filter changed this weekend but that didnt seem to help. I'm not getting a CEL so I'm really at loss trying to determine what the issue might be. Any ideas? Thanks!