Major Tom

I have 2020 3500 also, but have not seen your problem on my truck. I'd check the fuel filters and try some fuel injector cleaner before taking the truck back to the shop.

Take a look at what the iDash offers as monitored parameters. The first one I put on my iDash was current Transmission Gear Number and Torquer Converter Lockup. The next in line were: 2. Fuel Tank Level 3. DEF Tank Level 4. Percent Particulate Filter 5. Engine Coolant Temperature 6. Transmission Oil Temperature 7. Fuel Flow 8. Percent Torque

Upfitter switches are either always have power or powered on when the ignition is on. They are controlled with two fuses that connect three/two of the upfitter circuits. There is no timer, you will have to go to another fuse block for the timed off function.

Had the same problem with a tri-axle fifthwheel. Solution was to create another trailer profile, relearn the TMPS and delete the old profile. Record mileage and any other stuff from the old profile before deleting.

I ran mine along the driver side frame rail. Plenty of other wiring harness to zip tie to. Terminated under the tail light area, you can pull the tail light out for extra working room. How much power (Amps) are you going to be drawing from the plug in the bed? The longer the run, the longer (continuous) the current draw, and the lower the voltage drop you can tolerate, the bigger diameter wire/cable you will need. The dual battery Diesels have several places to pull power from, some using mega fuses if you want to stick with using a fuse. I haven't looked at the gas battery fuse block.

When one battery goes bad in a dual battery system, it will put more load on the good battery bring it down too. Both batteries should have been replaced together. I think you will find that the oldest battery is now the "bad" one and needs to be replaced. Unless both batteries are replaced, in about four to six months, you will see the same problem again.

Could be the anit-theft (Trailer) detection system. May be working as designed. look at the last paragraph on the below page. https://www.gmc.com/support/vehicle/entertainment/apps/trailering-app#:~:text=If the trailer's wiring harness,to help discourage trailer theft.

Just get the pillar mount from Banks, it matches my 2020 HD AT4.

On my 2020, that fifth wire terminates near the third brake light.

Seats might be the same but you are asking your question in the HD forum.

Start another thread, don't hijack this one.

You might want to lookup "Safety Locks" in your owners manual too.

Text below is from NHTSA Check for Recalls web page: "Oct 24,2024 Manufacturer Recall Number N242454440 NHTSA Recall Number 24V797 Recall Status Recall Incomplete, remedy not yet available Summary General Motors has decided that a defect which relates to motor vehicle safety may exist in certain: 2020 – 2022 Chevrolet Silverado1500/2500/3500 and GMC Sierra 1500/2500/3500 and 2021 model year Cadillac Escalade and Escalade ESV, Chevrolet Suburban and Tahoe, and GMC Yukon and Yukon XL vehicles equipped with diesel engines. A transmission control valve in some of these vehicles may be susceptible to excess wear over time, resulting in a gradual loss of pressure within the valve that can cause harsh shifting. In rare cases, the rear wheels may experience a momentary lock up. If the rear wheels lock-up momentarily while driving, there is increased risk of a crash." Yes, my truck is on the list. Had some bad sensors replace on the truck last week and the dealer said they (GMC) did not currently have a fix!

Ditch the fifth wheel and go with A Reese Goosebox or a Gen-Y hitch. Then you have less than 25 pounds in the bed of the truck, which can be removed in less than five minutes.

Just check to trailer screen after you start rolling, and then go back to your map screen. If you set up the max pressure, the truck will let you know in the DCI if a tire gets hot or pressure goes too high. It saved me twice on our last trip chasing the eclipse from Arizona to central Texas and back. I already drank that beer when I gave up troubleshooting and just deleted the old profile and started with a new one!