I Too have a 2018 Silerado 5.3, 6 speed. This is my issue.... On first thing in the morning startup the truck runs fine a with no issues. After sitting in the parking lot at work until 12PM, which is 5 1/2 hours later, on start up the truck, acts like it is skipping, and you can see the rpm needle actually "flutter". Took into the dealer of course they say nothing is wrong and all is fine, I told them to wait and run the truck after sitting for a period of time, the service guy said they did and had 2 others drive the truck and did not see anything wrong with it. Like I told them from the beginning if you mash the peddle you will not feel it, it is when you basically let the truck take off on idle to just touching the gas pedal. They looked at me like I was crazy, I would like to get this taken care of, it seems a lot of others have the same issue and GM does not want acknowledge it. Any thoughts?