TL;DR: I drove 2,941 miles from South Florida to Southern California in my brand new Sierra 1500 AT4 Duramax and pulled my 4,400lbs pound boat. I experienced no drivetrain issues other than running out of gas which was my own fault. I kep the rpms mostly at 1500-2100, averaged 12.6 mpg, consumed 11-12 gallons of DEF and had no cooling issues under the load and in the 118F heat of the Californian desert for the prolonged time I was driving. The trailering app and trailer tire TPMS system paid for itself and was a great tool for safety! DEF gauge may not be accurate to read when towing, rather go by the mileage warnings that display on the dash. Adaptive cruise control disengaged briefly but was able to re engage after turning the truck off and back on again. I am very satisfied with the performance I experienced and overall truck and have had no issues thus far with the drivetrain (6,054 miles on the clock).
Hey y'all, I wanted to put some info out there about the trip I just made this week from Boca Raton, FL to San Diego, CA in my brand new 1500 AT4 Diesel to include performance numbers, issues I encountered, good, bad, and otherwise. I was a little on edge seeing as I did a decent amount of research on the new duramax before I bought it in July and there are definitely some issues out there that are yet to be addressed, however I had to move for my new job so here goes.
Google Maps put the trip at 2,611 miles (4,202km) from my parents driveway to my new place but my trip clock read 2,941 miles (4,733km) due to stopping in to see some family along the way. I had 3,110 miles (4,989km) on the clock before I left. Note that my backseat was full of boxes and my bed was mostly empty except a weatherproof toolbox because I don't have a tonneau cover yet and did not want my items exposed to the elements or sticky fingers for the five days I was on the road. I was also towing my boat which is a 20 foot center console on a tandem axle trailer with dual axle hydraulic surge brakes. The boat and trailer combo weighs 4,400lbs (1995 kg) as indicated by the weigh scale I stopped at in California and my WeighSafe drop hitch with tongue scale. I spent the overwhelming majority of my time at ~1500 rpm while on cruise control at 67-mph but would jump to ~2100 when gradually accelerating.
I left on Sunday afternoon and drove 225 miles (362km) to Daytona Beach, FL mostly uneventful despite my DEF warning popping up saying I had a 1000 mile range. On Monday, I drove 514 miles (827km) uneventfully seeing some family and friends in the Panhandle of Florida. The only eventful part of this leg of the journey was the DEF message popping up in the morning saying I had a 300 mile range approximately 150 miles after the 1000 mile warning and a speed limited soon message shortly after the 300 mile message. I figured I would use more DEF while towing but I hadn't put much thought into exactly how much I would use while planning my trip. I will talk more about DEF later. Tuesday I drove 537 miles (864km) from Milton, FL to Houston, TX uneventfully. Somewhere around San Antonio, TX I got a message that adaptive cruise control has disengaged. I was able to switch to regular cruise control but still don't know why that happened. I was able to re engage adaptive cruise control later in the day after I turned off the truck at a fuel station. Any thoughts would be appreciated here if you have experienced something similar. Wednesday is where the fun started.
About halfway between Houston and Fort Stockton (508 miles, 817km) I got a low trailer tire pressure message on my dash. My truck came with 4 trailer tpms sensors I had installed into 4 new tires on the trailer about a week before I left because I figured why not. the tires are filled to 50psi as per the sticker on the trailer and the message showed front right had 35 psi. I figured all was fine and it was an error message as I had already driven over 1000 miles with no issues but I decided to stop and check at the next exit as I noticed the pressure was steadily declining. I pulled off at a Love's and went to check and could hear the air coming out but couldn't see a nail or feel the air. Regardless (after re parking in the shade at 102F outside), I took the tire off and lo and behold found a 3 inch nail in the tread near the edge of the tire. Within 15 minutes I had it plugged, refilled, reinstalled, and ready to go. That right there ladies and gentlemen justified the $85 I paid to install the sensors. Had I not known of the diminishing air pressure I surely would've had a blowout at the most inconvenient location and had to put a spare on in the heat. So that sold me on the trailer tire TPMS system, cost to install already paid for itself by saving me from having to buy a replacement tire.
On Thursday, the plan was to go from Fort Stockton, TX to Tucson, AZ (558 miles, 898km). I was about 30 miles away from my next planned fuel stop when my fuel level low light came on but I didn't think anything of it as I would be stopping about 20 miles before I ran out of fuel. When I pulled off at the only fuel station in the area (Akela, NM) which GasBuddy showed had diesel, I discovered much to my dismay that the station did not have a diesel pump. I knew I was probably screwed but didn't really have a choice but to shoot for Deming, NM which was 24 miles down the road. My fuel level read low so I reduced speed to improve economy and hoped for the best. Worst case scenario I run out of fuel much closer to an actual city which would reduce the time it took for a fuel delivery service to reach me. 5 miles out of Akela, a car flags me down and says something blew off my boat so I pulled over and saw that my bimini top had blown off. I figured my best course of action was to drop the boat on the side of the road and turn back and try to find it. because there was no way I'd make it to Deming after turning around with the boat. Anyways, I had to go back about 3 miles to get the bimini from the middle of the road before going back. I decided to leave the boat, get fuel, and come back for it. The boat has a tracker so I could ensure it didn't get stolen plus i had 2 tongue locks on it. I made it about 12 miles before I heard a sound from the engine that sounded like i hit debris on the road, a message popping up that said speed limited, pulled over and kept the engine idling while I inspected the truck for damage and could see none. I turned off the truck to restart it and try to get back on the highway but it wouldn't crank. I called roadside assistance from the myGMC app and a guy called me to confirm that I needed diesel and was out to me from Deming in about 20 minutes. Fueled up, started, but had a check engine light so I brought it to the Chevy dealer in Deming to get checked out and ensure there was nothing seriously wrong other than running out of fuel. It was just some computer errors from running out of fuel, had them cleared, and left for no charge. Filled my tank at the nearest fuel station, turned around got my boat, and continued on my way after a 3 hour delay and made it to Tucson just in time for happy hour!
Friday, I finished my trip to San Diego about 407 miles (655km) uneventfully despite temperatures reaching 118F outside. I was monitoring engine temp which was regulating well between 190 and 205 and tranny temp which kept between 185 and 203 depending on the grade. No issues at all with cooling or performance. Honestly the torque was really impressive on the 6% grade that stretched about 35 miles up and down.
By the time it was all said and done, i averaged 12.6mpg for the entire trip although I was getting about 14-16 after I had the bimini top stowed in the bed on the truck reducing the drag of the boat. I had to put in about 11-12 gallons of DEF throughout the trip to top off my tank at the end. I found that the DEF gauge was not displaying accurate levels because when it displayed red Low and no bars it took 4 gallons before overflowing despite the tank being about 5 gallons. The range of the DEF was not linear. It showed 300 mile range at 5 bars but dropped to red and low almost immediately after reaching that point. I learned to go by mile range not necessary gauge level and just fill up at the 300 mile range message. I am satisfied with the fuel economy i saw and was very satisfied with the performance and power available when needed thanks to the diesel. Overall very satisfied with the performance of this truck as I have had no issues with the drivetrain (knock on wood). Feel free to ask me specific questions and I will answer them as soon as I see them!