Cavalier 92 Convertible, problem with the trans

Hello,

I have a 1992 Chevrolet Cavalier convertible with a 2.2L engine. I'm seeking your advice because the automatic transmission makes a clunking noise when I start the car and shift gears. I was told that a bone-shaped engine mount needed to be replaced, which it was, but the noise persists. It only happens at the beginning; once I'm driving, the gears shift perfectly.

Another issue is that when I'm on the highway, sometimes the transmission gets stuck in 3rd gear, and when I have to slow down for a speed bump, it doesn't shift back down. I have to manually downshift to 1st gear, otherwise the car stalls. At first, it happened very infrequently, but now it's very common (it only happens on the highway; it hasn't happened in the city so far).

I'm asking for your advice because I've had bad experiences with some transmission shops and would like to be better informed.