Brand new 2019 Chevy 2500HD Duramax. 1500k miles. Hooked up to my 2016 Nash 25C travel trailer which was probably about 7.5-8k loaded. First pull with the new truck. Which I have been loving this truck by the way. Was cruising along going over a grade, but uphill nonetheless, and was doing about 60-65 mph. I felt like the truck was in a higher gear than it should of been, cause I was at about 1500-1700 rpm, so I notice “hey, I didn’t put it in tow/haul mode” so I did. No big deal. I stepped into it a little, the tranny dropped a gear and now we’re climbing this hill. WELL... as I came off the pedal, and honestly I’m not really paying that much attention cause I’m on cloud 9, but I think I may have come off the pedal and then went back on it... WHAM! As you described in your original post. Immediately my check engine light comes on, I get an alert on the display that the truck is in a reduced engine power mode, and thanks to my MyChevy app on my phone, I simultaneously get an alert on my phone that I need to get the engine/transmission serviced within 7 days. 😳
Sooo... I get down the other side of the grade cause I’m in shock, listening for something outside the truck to give me an indicator that I’ve somehow grenaded the tranny. Nothing. I’m rolling. Engine is purring. Aside from being in reduced power mode, nothing else is happening. After I stopped at a stop sign once coming off the freeway, I’m positive I’m in “limp mode.” Anyway, I make it to where I’m going and I drop my trailer. I shut off the truck and restart it. Check Engine light on. No “limp mode.” No reduced power mode. I immediately drive to the dealership where I bought the truck 29 days earlier. Truck drives fine all the way there. Check Engine light still on though. I get to the dealer, shut off the truck. Service tech comes out, starts the truck... Check Engine light now reset. Figures.
2-days later, they found 2 historical codes (intermediate codes they say). I’m gonna get the actual codes when I go back in, but Tech is saying everything checks out and to come get the truck. Thanks bro!
So, I’m gonna go get it and drive it. These posts have been helpful. Especially misterwizard’s. Thanks to everyone else’s too. I’ll update once I get my truck back and get the codes. After reading these posts I guess I need to just drive this truck more so Mr. Allison can figure it out!