My car was towed to Holt on 23 July 18 to have the transmission fixed. Today (9/19/18) I took my car to another shop for unrelated issues.
The mechanic there pointed out my engine mounts were bad.
As they replaced them, I was shown a new one and one of the old ones, which I have kept.
I have put 606 miles on my car since having the transmission replaced, so there's no way this just suddenly happened. Either their mechanic was incompetent, or they were just trying to get money down the road when I started having transmission issues because of the motor mounts.