I have a '19 and it does the exact same thing. It's usually when I am coasting to a stop, under little or no load. I live on a hill and leaving the house I always coast down the street to a stop sign and the engine "chugs" or "bounces" to a stop. Interestingly, although it can jump up in rpm's it doesn't cause any surge in the drivetrain, I still coast. I have only had it put power into the drivetrain a couple of times and both times I was going up a slight incline coasting to a stop.
The truck has 10k and has done it since day one. I plan on scheduling a visit with the dealer but wanted to get a few miles on the truck to see if if would resolve itself - it hasn't.