Okay, little back ground.
Christmas day, drove the truck fine, shifted great no signs of slippage.,
Went to go back in a parking spot no reverse, but i had forward gears.
Drove it around the parking lot lost forward gears, pushed it into a parking spot and let it sit, went back out after 30 min shifted through all gears as normal, with little to no slippage. It has repeated this process about 4 times now. Just looking for some opinions on what could be wrong, thanks!