LCH14

Looking for help! 2019 GMC Sierra 1500 - 5.3l 4x4 8l90 61k miles - truck is in Arizona, was over 110 outside on Monday when this whole situation transpired. Never had any major issues with transmission until this point: Truck sat outside my construction office for approx 1 hour idling before I realized, ran around the job site wrapping some things up for the day and then left. Went to get food and sat in the drive through for approx 30 minutes idling. As soon as I pull out of the drive through and onto the main road, rear tires lock up and feels like transmission fell out of the truck. Shifted to park, shut the truck off and tried again, same thing happened. Was able to reverse into parking lot (truck slammed into reverse). Let the truck sit turned off for 10 minutes before trying again, but it continued to happen. Towed truck back to my house. Highest the trans temps reached was 198. Friday, after work I start looking into the situation. Truck sat in my driveway untouched all week. Truck is now driving like normal, transmission doesn’t get over 185 degrees when trying to heat it up. Got up to 60 multiples times with no issues, no issues accelerating, only down shifted hard into first one time at 185 degrees. Does anyone have any insight? Never through a code or a check engine light. Truck has never been used to tow either. No transmission services at this point.