1974 Plymouth Valiant - 2013 Dodge Dart - 2013 Chrysler 300C
I would add two things.If I were you, I would look into getting an attorney who specializes in auto repair cases, and/or take this to small claims court if either repair shop refuses responsibility. I would also report both to BBB, and your state's attorney general for possible legal action. As you mentioned, you were just earlier driving at highway speeds, and this could have not ended well not just for you, but the countless other motorists who may have been injured or killed as a result.
First, BBB is a con job in some states. They report cases closed if the business owner pays their fees and says it was closed, and they won't reopen it. In short BBB is just one option.
Consumer Affairs departments are strong in some states, weak in others. They're not in GMG's list so I added them.
Finally, if it's within the 90 days (or is it 60?), you can also dispute the charge with your credit card company. This is a little risky since every state has a mechanic's lien, but you can argue they did not actually provide any services, and therefore should not be paid. The one time I had to resort to this, they disputed my dispute, but I had another mechanic sign a sheet of paper saying timing belts were supposed to last longer than ten days, and the card people agreed.