So for anyone who following or wants to know. Here what I have so far.
If you have a 6.2L 2023
After a week at the dealership Chevy/GMC/Cadillac combo, the tech heard the sound and could easily reproduce it the squeal. They also confirmed that the squealing is gone with the truck in L9 mode which deactivates the DFM.
They couldn't identify the location of the squealing while on the lift since truck doesn't do it when it's not under load.
They got the tech like involved. Tech like told them to take another 6.2L 2023 on test drive. The dealer had a Escalade on the lot with 100 miles on the odometer. They drove it and reported back that the squealing was also present on the Escalade.
The tech line deemed it a feature of the truck and no repair was authorized. The tech like also said that GM made changes to the programming of the DFM for the 2023 model years. What changes, who knows.
Today, I went to a different Chevy dealer that had a new 2023 Premier with a 6.2L on the lot with 12 miles on the odometer.
I drove it and it ALSO squealing. The dealer will get another 6.2L in a week. I'll drive that one as well.
I have not driven a 2023 5.3L, but it appears that if you have a 2023 6.2L, the squealing is normal.
If someone else has a 2023 6.2L and could drive with their driver's window down and verify if they are also getting the squealing when slowing down, I'd appreciate it.
1) If you smoothly drive up to 25-30 (causing the truck to switch to v4) and slow down gradually to a stop, when the truck slows to the near stopping point, the engine will switch back to v8 and the squealing can be heard.
2) If you cruising at 30-40 smoothly with little torque on the engine, the truck will operate at v4. If you tap the gas quickly (causing a shift to v8) you can hear squealing.
3) On could start up, you can hear the sealing from the engine for a minute until the engine revs back down and then it goes away.