2015 GMC Sierra 1500 4×4 with 96k miles. I have not driven this truck hard and always upkept maintenance, I changed the oil yesterday morning and didn't see anything out of ordinary when i was underneath and then i start the truck last night and it will only move for the first maybe 20 seconds and then it's like the transmission goes out and the truck will roll freely and has no gears, makes noise for maybe 30 seconds after you start it and will go into gear and try to move and then lose gears again. Found nobody else online having this issue, I've had it since 18k miles and have taken care of my baby. Any info will help thanks