When purchasing the truck in late December 2021 with 18k miles, I don't recall this occurring. Since then, June 29th, I've put on 16,000 miles. I do my oil changes every 2 months or 5,000 miles per the recommended in the service manual, and they are always done at GMC Dealerships due to the cost, and convinence.
This morning (6/29) I've turned on the truck, and I usually let the truck idle for a few minutes before driving. I noticed that in the drivers seat, some sort of vibrations coming from the engine bay. I noticed additionally that the RPMs are a little less than the number 1,000RPM. My feet are not on the brakes or the gas pedal. I immediately turn off Auto Start Stop each time I get into the truck, I find it annoying. When driving no other vibrations occur, truck drives like a dream.
In April, I noticed the vibrations again but this time it was not upon start up, it occured when I got to my destination and say idle in Park. I was curious, so I turned off the truck and turned it back on, and no vibrations then.
I've been reading on fourms that other users experienced, spark plugs needed to be changed, or injectors Etc. I should note, I only use the recommend gas 87. I've ran 91 before, but due to gas prices increasing, I don't see the benefit. Being that my truck is just short of the factory warranty (36,000), I've thought about bringing it in to get looked at by a Service Tech at a local GMC dealership.
I've always been taught to drive a car/truck until you see a CEL then bring it in, so they can actually diag.
TLDR: Truck vibrates at random times, only at idle. Potentially DFM?