2003 Chevy Lumina my car suddenly stopped

2003 Chevy Lumina mileage: 37,000. Last summer I was cruising at about 55 and my car suddenly stopped. It had broken the timing belt and the timing chain. I've taken it to (2) different repair shops 4 different times to try to get it timed right and they just can't seem to get it. It runs great in drive but when you put it in over drive, it vibrates until your reach about 55 mph. I've had the spark plugs and wires changed but it still won't run right. They can't find the right book with the diagram for the spark plug wires. What else could be the problem and where in the world can I take this car to get it running right?