I have a Jeep Grand Cherokee 2016, 76k miles, last transmission fluid change was less than a year ago, before the change, the transmission wss shifting hard, mechanic when he made the fluid change, before, he checked the loquid for particles, it was clean, he changed the liquid and it helped somewhat, after some time it ran fine just a little bit rough shifting, no codes or anything, today coming from work, was in heavy traffic, it started shifting harder because of the starting and stopping, eventually when I got close to my home noticed it got stuck on the 4th gear and went I think safe mode, does not shift anymore, when putting it in reverse it blinks the R on the shifter and wont shift. Code P0974 popped up on OBD. What can it be?