Only issue so far was an emissions code that showed up about three hours after I left the house and was speed limiting, thusly ending my planned Harlan trip a few weeks ago. Dealer replaced the DEF pump in the tank and the harness that feeds it, and it's been good since.
With the rockwell buggy and a Polaris Ranger on the trailer it was the heaviest I have pulled, and I must say I was expecting a little more towing prowess. It slowed down on the long mountain runs that my 3500 Duramax dually would fly up with the same load. I guess the extra 4,000 lbs. the truck itself weighs doesn't help (11,450# curb weight as recorded on truck stop scales).
Tuning is pretty pricey but I suppose it'll have to be done for me to be satisfied with it.
https://duramaxtuner.com/diesel-tun...ne-incl-hardware-&-credits-l5d-2019-2021.html
On the plus side it rode much better with the trailer hooked up, and even once disconnected the rear springs seem to be broken in or something, way less bouncy. The Allison 2000 trans is amazing and the exhaust brake seems more effective than on the light duty trucks. Cab is as quiet as a half ton Denali.