We were stopped in a construction zone & it took about 45 minutes to go about a mile. It was over 100 degrees so I kept it running. Every 3 to 5 minutes might move about 50 feet. Never got fast enough to use the gas. It's a 2015 A8, Z51 Callaway. After about 1/2 hour of this I heard a loud bang and at the same time the car lurched forward. I thought I was rear ended and got out to look and I wasn't hit. It did it 3 more times before we got out of the Calif. construction mess. We continued to Monterey, CA and back to home and it never did it again. It has been driven about 800 miles since then with no problem. When it was happening I never thought to check the A8 temp on the DIC. Think it was just 2 hot? Should I get tranny fluid changed?