I have a 2012 traverse. There is a shudder under acceleration that starts at 30 mph and will continue to 40 mph were it goes away. I don't think it is a transmission issue as the transmission will shift with no affect on the shudder. this issue started when I had about 97000 miles and has gotten worse. Current mileage is 194,000. The issue did start right after a transmission pump seal broke and I had the tranny pump rebuilt. I brought it back to the dealer numerous times. They blamed brake rotors, tires etc. All have been replaced a time or two since then.