South Louisiana here. Got the "Service Transmission. Unable to shift soon." message on my 2021 Tahoe a several weeks ago. Currently at 51,000 miles. Temperatures were low outside, but I don't recall how low (low 30's I believe). Message cleared itself. Message returned about two weeks later. I've contacted all of the dealerships in my area and none of them can see me before the end of February. No loaner vehicles available either. I have not noticed hard shifting, grinding, or any other signs of trouble with the transmission. One dealership service department said they are getting a ton of calls for transmissions with this message. This morning I also got two other messages, "Service Lane Assist" and "Forward Collision Assist Not Available". To say I'm worried is an understatement, but I was told by two dealerships that if I brought my vehicle to a transmission shop it will void my warranty.
