2019 Sierra 1500, 2WD, I4 turbo, 8 speed. First leg of a 2000 mile trip, driving thru California desert on cruise at approx, 80 MPH. Very light traffic, so cruising along, slight incline, when "Yank", or "shock", DIC lit up with "service parking brake" then "service ESC". Then, nothing. Truck seemed fine, continued on cruise at 75-80 MPH. Within 50 miles the symptom happened again, and the DIC again showed those two screens, also the "check engine" light started flashing, so as soon as possible, I pulled into a McDonalds and let it sit for about 20 minutes. Got back into truck and everything seemed normal, no lights, nor any noticeable issue. As there was no dealership available, I continued onto the next large town, where by that time, the "yank" had happened twice more and the check engine light was on hard. So, parked the truck and rented a car for the remainder of the trip.. At that point the truck had 2,560 miles on it. A dealership in Carson City, Nevada, picked up the truck and took it to their dealership, where the only thing they could find was a PO300 code (Misfire). We tried to explain what had happened, but the service writer didn't want to hear it and diagnosed the truck as having gone into "Limp" mode with reduced power. Never happened! We tried to get them to drive the truck and try to reproduce the conditions which they said they had done, said they'd had it all over the local hills. When we got the truck back (via GM's "Re-unite" Program which was great) the odometer showed one mile more than when I parked it, so obviously they didn't even drive it. So, after Google surfing, we now know that there are problems with the 8 speed trans, but I'd have to say I think it's more of a brake issue than trans. Anyone else experienced something like this???? I could really kick myself for not grabbing pictures of the dash as I can't find any references at all to what I saw.