I've got a 2020 3500 GMC Denali with 27k mileage on it. This same problem just sent this one to the shop. Hard shift if it would engage at all. High rpms that would barley move the truck. Also this started when in 4 wheel drive and the throttle was surging if the truck slipped in the snow. Strange to say the least but it the first issue I've experienced. Been a good truck otherwise. Did they every figure yours out?