AT-FORE

todd308 - I have definitely noticed 1&2 on your list above. If you end up investigating the exhaust valve and determine that is not the issue definitely keep us updated. I know these trucks have very sophisticated drive trains. My transmission shifting has actually gotten better. Some random hard down shifting occasionally but nothing out of the ordinary. When I test drove it, I felt it shifted in very odd ranges and in times when I thought it shouldn't, but I think that is all part of the 10-speed transmission. Maybe I have gotten used to the shifting at this point but I feel that aspect has gotten better with miles and my driving style. I have about 1500 miles on it now. 3, 4 and 5 on your list I don't think I have had an issue with. If you think something should be working and its not I would surely take it back to the dealer. My dealership was very forthcoming about telling me to come back if I had any issues or questions. Another "gremlin" on mine is the buzzing whenever any door is opened. I have researched this and I believe its the fuel pump priming, but my truck does it when any door is opened or even the tailgate is dropped after sitting for 15+ minutes. This is a very odd feature for a vehicle in my opinion.

Update to my 5/26 post... I finally got my Sierra 6.2 AT4 up to the dealer to take a look at the squeak. The repair mechanic seemed very knowledgeable and did a ride along so I could reproduce the issue. The squeak was very prevalent at autostart/stop and it happened right beside the building so he could very clearly hear it. Unfortunately he indicated it has to do with the compression exhaust valves which are associated to the AFM (Active Fuel Management) system and the cylinder deactivation functionality. He told me that given more people are buying these vehicles as "family vehicles" causing some give and take in vehicle functionality. Consumers want better fuel economy hence the squeaky exhaust valves, and active fuel management functionality and the super annoying autostart/stop. Apparently, consumers want a faster start/crank time, hence the buzzing when I open the door to prime the fuel pump. Regardless, I still cant believe GM would put a vehicle into production with this kind of squeak or noise... why not put a little more R&D into the valves so they don't squeak when used on a luxury truck? The mechanic also said installing an exhaust system WILL NOT solve the problem as the valves are right under the headers on the engine, still int he exhaust pipes but close to the engine. It seems the only way to get rid of this squeak would be to have someone deactivate the whole AFM system, which apparently can be done but voids warranties. Well guys, I guess im driving a super bad ass AT4 with a "normal" loud squeak..... which I hear every time I drive it.... (headbang)

I just purchased a 2020 AT4 with the 6.2, 10 speed. I have about 720 miles on it and have already had it at the dealership for the exact same squeaking noise. My dealership told me they could not replicate it and the noise is either the high pressure fuel pump or dry sump oil pump. I know neither one of them are the culprit because the truck does it on startup and constantly between 1000-1600 rpm when driving. Its not the fuel pump and its not the oil pump. It sounds like a bearing and it is extremely annoying. I drive a lot in the mountains on slow winding roads and the noise is extremely loud in this type of environment. I also thought about putting exhaust on it thinking it would take care of the squeak, but I'm glad I read through this forum before I spent the money. It sounds like this squeaking noise is "normal" but does there is still no true answer. Its quite embarrassing when I spend this kind of money on a truck and the first thing my wife says is "It squeaks, whats that noise", I sound real dumb when I tell her "Oh, they say its normal, don't worry". I went from an 07 Tundra to this and there is no comparison, the AT4 is amazing, but this squeak is absolutely obnoxious. I have never owned a GM vehicle but at this point, I hope I made the right decision. I will take it to the dealer once more and have them ride along for them to hear. I will also contact the GM social media posted in this forum.