2019 terrain lugging

Purchased leftover with 400 miles on it. I have found the transmission does not downshift properly when approaching any kind of incline. This has a 9 speed transmission with a turbo 4 cylinder. This unit should shift flawlessly with no effort. Instead the RPM's drop so low the engine lugs causing a horrendous noise in the terrain. Have had it to the dealership several times, spent time with the regional technician, and the latest, the aftermarket rep. All have experienced the lugging and nobodu can do anything to correct the problem. All I've gotten is lip service. GMC supposedly has brilliant technicians but claim there's nothing wrong and it's just a characteristic flaw in the vehicle. They're response, you'll get accustomed to it. I'M NOT!! This may work on their computer, but it does not work in real life!!!!!! DO NOT BUY
For the people who are experiencing this should contact GMC & let them know your experience. It seems there are complaints but not enough to warrant any action.