NHTSA Complaint #11644738 — 2020 GMC SIERRA 2500

While towing my dump trailer early in the morning for about 20 minutes I noticed sudden hard up shifting and down shifting in some gears on flat surface roads. I then proceeded to approach an incline hill about a 5% grade and then, what I've recently learned, my transmission locked up and released for a split second. The roads were slick so it didn't seem too harsh, I continued with no incident for another 40 miles and then it happened again while pulling up a 7% grade in a left hand sharp turn at 40 mph. The truck fish tailed and jack knifed my trailer on the left rear side of my truck and the front left side of the trailer. I was on a one lane road and had to continue until I reached my detitanation, I slowed and maintained a speed of 45 in order to prevent it from happening again but it did it 5 more times before reaching my destination. I'm currently scheduled to have the transmission checked on 02/27/2025 at Peterson's Chevrolet Nampa Idaho. In the meantime, I have no means of using any of my trailers.