Today I noticed when coasting @ 55 that the transmission seemed to be downshifting and upshifting every 10-15 seconds. Also under medium to heavy throttle is seems like the car is struggling ie. Stuttering slightly like its missing spark or something. Also its shifting hard at stops and sometimes between gears. Weird thing is when I put the car into manual (paddle shift mode) the problems I described above are non existent. Car shifts fine and under wot no hesitation. Any ideas?

2005 comp g