Q: Hello, I have a 2002 Pontiac Grand Prix that sued to be a GTP. I gave a mechanic my car over three weeks ago so that he could put

Hello, I have a 2002 Pontiac Grand Prix that sued to be a GTP. I gave a mechanic my car over three weeks ago so that he could put another engine in. Initially my car was making a knocking noise, so he said I needed a new engine. Well after three weeks, he said he was finished and made me come get it even though he said he would bring it to me. I test drove it first and the steering wheel was hard to turn but he said it just needed power steering fluid. Then I gave it another drive and it was driving fine until I put the car in reverse and then back in park. The car kept shutting off, he said it was just the air flow and was supposed to fix it. Well, I ended up having to drive my car from Oklahoma City to Norman and the entire drive, the engine kept shutting off. I couldn't even drive a mile without the engine cutting off. Near the end of my drive, the car started smoking. Can anyone help me?

My car has 135000 miles.
My car has an automatic transmission.