Help

I've had my car looked at from 2 different mechanics at 2 different shops and we can't seem to figure out what the problem is. My bravada will run great for the first hour or 2 of the day then my service engine soon light will start blinking and it will start to chug kinda. It idles very low when parked or stopped. It doesn't do it constantly. The light will blink and my car will run like crap then do fine for a few miles then mess up again. I've changed all plugs and 2 cylinders and have did a couple other things but nothing is fixing the problem. Please help me so I can continue to go to school and have transportation for my children.

Thank you in advance