This has been an ongoing issue. Truck currently has 45,000 miles on it. When driving on the interstate for 30 minutes, transmission flutters causing the cab to shake. It feels like running over rumble strips. Flutter lasts for several seconds and gets worse (longer duration, harder flutter) as time gs on. Dealer won’t diagnose it because no codes are recorded. No dash lights light. The only indication is the flutter itself. Chevrolet cust support says their hands are tied – it is the dealers responsibility. The dealer will not devote personnel for 30 minutes to replicate the issue. Issue comes out of no where startling the driver – not safe. Your first reaction is either to brake or gas to stop the flutter/shake. Flutter is stronger as time gs by. This issue has been identified for other years of the same vehicle, and several GM vehicles. It is still an issue in 2020, but not recognized by GM. Multiple complaints are on the internet for this issue by other 2020 Colorado owners.