I've got a brand new '17 GT with the performance package. It just ticked 500 miles. It seems like I've got a small (it's hard to describe) hitch when going from 1 to 2 and 2 to 3. If I shift slow it seems like I can feel the gears stop and sync. Once I move out of the gear and back in it's smooth like butter. Maybe the gears are not syncing correctly. It's not bad, just feels not quite right.
Took mine to my dealer (I work there) and they checked the condition of the fluid and it was clean. I am keeping track of it to see if it gets worse. I read that an aftermarket shifter cured someone's problem in this forum, but that would be out of your pocket, not warranty repair.