I did the EXACT same thing in May of this year. I had ordered a Sierra AT4 1/2 ton 4x4 with the 3.0 in December 2020. While we were waiting we decided to order a 27’ Airstream that weighed in at 6800 lbs max. As luck would have it, the truck came in two weeks before the trailer was delivered. I really enjoyed the 3.0 power and economy on the highway. Sooo smooth! According to published data of payload and towing capabilities, I felt the AT4 would be close to capacity but “should be OK”. I picked up the trailer installed a Blue Ox Sway Pro and headed 70 miles home. Although the AT4 had more than enough torque and horsepower to pull the trailer, it was evident I was at max payload. A stop at a Cat Scale confirmed my seat of the pants feeling. I was over my 1430 lb payload by 290 lbs and close to max rear axle load. I was at about 75% road ready loaded. When I got home, I knew I could not travel 10-12k miles a year towing with the AT4. Very disappointed, it was evident I had to trade up to a 3/4 ton P/U. To my surprise the AT4 increased in value due to the chip shortages that were delaying new truck deliveries. In a stroke of luck 4 weeks earlier a customer had cancelled his order for a 2021 Denali 2500 because he did not want to wait another month for delivery. I jumped on the opportunity and I had the truck in 8 days. The price difference after the trade was $9.5k! I’m at 16k miles with the Denali. It has a 3055 lb Payload and that monster 6.6 Duramax! I’m extremely lucky and happy I decided to upsize. The trailering difference is like night & day.
It's a faulty trailer light module on the truck. GMC replaced under warranty.
Hi! (Sorry about the long winded narrative in advance). I'm been dealing with a Trailer light issue on my 2021 Sierra 2500 HD hoping for suggestions. I plug in my 7 pin connector from the Airstream to the truck. As soon as the connection is made the marker lights on the Airstream come on. However, the truck light switch is in the "off" position. I jump in the truck and start it. I get the two messages below on the dash message center and the center stack. Shut it off, disconnected and reconnected the 7 pin plug. Restarted, then ran the intergrated lighting check and verified that all of the Airstream and Truck brake, signal and tail lights function as normal. As soon as the trailer light check is complete, I get the messages below again. The truck shows as connected and trailer braking system is active. The initial event took place at an Airstrean dealership 1500 miles from home. Up until this point I had been towing for 8 weeks and 3200 miles without any issues. Based on the truck's fault message, I sought out a service tech to check the Airstream wiring and male connector. I was with him as he went through the steps on the Airstream side. All Airstream connector circuits checked out. He then plugged a scanner into the Truck's 7 pin female connector. He received a "LT Lamp fault". I thanked him plugged the trailer back into the truck and and headed to close by GMC dealership. Sure enough, the GMC service tech who offered to do a quick check got the same "LT Lamp" Fault light on his scanner while plugged into the truck's 7 pin connector. Unfortunately, the did not have a schedule opening for a few weeks. I was on my way home so I decided to head home and make an appointment at my local GMC dealer to trouble shoot the issue. That night I decided I needed to disconnect the connector as the maker and tail lights of the airstream were still on after the truck was shut off. I did not want to kill the truck battery as I wanted to get an early start home. The next morning, I got up plugged the trailer into the truck. No marker ights. I thought, what ever issue occured the other day might have been reset knowing the truck lighting module performs some self checks. I ran the on board lighting test OK. Ready to go. Put it in gear and the trailer brakes were locked up. Unplugged and reconnceted the connector still locked up. I crawled under the truck bumper at the back of the connector looking for loose or broken wires. Nothing. Tapped on the connector, and the camper next door to me said "the lights came on". Sure enough put it in gear and off we went. I ran 1140 miles straight through from Carlock IL to Clermont FL stopping only for gas and did not touch the connector. Parked the trailer and brought the truck to the dealership this morning to chase down the issue. Well, as luck would have it, they found nothing. No codes, no code history. The connector receiver was fine. As I was told..I drove the truck to the Airstream and plugged the connector in. Bingo there were the fault messages again. To verify once again, the Airstream was not causing the fault, I swapped out the Sierra for my 2021 Jeep. Plugged the Airstream connector into the Jeep's 7 pin receptacle, no marker lights came on until I switched them on via the Jeep light switch. Also no connection issues all lights and signals worked. Has anyone dealt with a similar issue or know about any TSB's that might help remidy this problem? I've got a nice trip planned next month but can't go until this issue is resolved. Thanks in advance.
I submitted a claim to GMC Customer Service in an attempt to get an ETA on High Clearance Steps that did not show when my AT4 arrived. It’s been 16 days. I offered to take a credit to go get a different set boards. Crickets. ?
A word of caution. I ordered my AT4, 3.0L, 20", Satin Steel Metallic, Carbon Pro on 12/17 and picked her up 2/10. Only problem was no High Clerance Steps were shipped with it! These are dealer installed but shipped with the truck. Dealer says product shortage. No time table indicated. I did file a claim with GMC to make sure they have a record of the issue. BTW - This truck is beyond my expectations. Very happy with my decision to get the AT4 over the Trail Boss because of the 3.0L& Carbon Pro options.
Must be something to do with the 6.2L. I ordered a 3.0L AT4 on the same day. It’s In transit to dealership with 2/10 eta as of GMC Chat this morning. It sucks they leave you in limbo. I was very lucky.
Roger that! Thanks!
Do you have a link for gm chat?
Great info! Thanks.
Ordered an AT4 crew in Satin Steel with a 3.0 on 12/17. Haven’t heard anything yet regarding a VIN.Too close to the holidays. Tick, tock.
I test drove a truck on the lot. After that I was totally in lust! I ordered a loaded High Country 2500 HD. Currently at 4700 miles. Fit and finish is second to none. The 3.42's and that 10 Speed transmission provides smooth ample power and surprisingly good MPG. The 6.6 Duramax is a beast. But it can be an easy going highway cruise also. Recent 400 mile interstate trip empty showed 23.8 MPG at 75 mph or so. I wanted the 11,300 GVWR option which gives me 3044 lbs. of Payload. I can do quite a lot with this truck. Plan on towing a 30' Airstream. That towing camera system is a great towing and hitching aid. Really like the heads up display. If I had to say a negative thing about it would be that I can't find a home exhaust tip for it! Jump on one of these you will not regret it!
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