Update for everyone. Finally found a reputable shop with experience working solely on older GM’s, Cadillacs specifically.
When he heard the car run and start he immediately knew what was going on…the timing belt was installed incorrectly and the car was out of time. This was causing the noise, hard start, shuddering once TCC engaged, and vibration. He also fixed the horn and SWC (kinda). Three other shops couldn’t figure this out. I’m so relieved, cars running so good.
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