I have an 03 Monte Carlo. Put a new fuel pump in and then had to have injectors clean3d due to misfire in cylinder 5. Had that done and ran injector cleaner in gas till everything smoothed out. Runs nice once it turns over. Started having problems. Bringing my gf to work one night, my engine just shut itself off. Glided over to the curb, put it in park and started right up. Dropped her off at work and went to get gas. Wouldn't turn over after shutting it off. Lucky for me, a friend of mine pulled in and we put cables on it and kept at it and it finally turned over. I decided to put a new starter in it. Sometimes when it starts up its just fine. Most of the time it just won't turn over. Sometimes it turns over and it struggles for gas and stalls out. I can't figure out why it does this. It was such a reliable car till now. Please help