Transmisson

I got a fuel rail installed in my car. After New Years I discovered a gas leak, was told fuel rail. Rail was repaired within a week.
When I went to pick car up, it sounded funny, was told I needed pulley tension-er. When I started to drive off, car was barely moving forward, but drove good backing up. I backed car back to mechanic shop. Mechanic noticed. After a few minutes it would stop going forward, but, if you turned car off and restart it will go a couple minutes .this was done on mechanic lot. Transmission fluid was good. Help! cannot afford a transmission.