I have a 2015 GMC Yukon XL (140k), I was driving home from work, maybe 4 miles from my building and my transmission starts slipping. I pulled over, checked my fluid level. Fluid level is good and clean, no leaks. I put the truck back in drive and press the gas and the engine just revs, in both drive and reverse. When I put it in gear, you can not feel the transmission engaging. It will go into neutral, but that’s it. I am puzzled what it could be, any ideas?