Trans slipping or? Grinding noise left front? 2020 Silverado

[Kenbow]

Couple of questions, bought a used 20 with 35k on it, every morning or first run of the day I get a hundred feet down the road and the truck seems to slip into neutral or something, let off the gas , then it’s fine for the rest of the day??? Yesterday I got in a started backing out of the driveway and heard a grinding noise from the front left side it was intermittent and then slowly went away? The truck may sit for a few days between drives, I have 35,600 miles on it, so some insight would be welcomed. Thanks in advance 

[Transient]

We need more insight.  Let's start with what transmission you have.