2001 Chevrolet Lumina car starts jerking and stalls

2001 Chevrolet Lumina mileage: 70,000. This problem only occurs after I have driven 25-30 miles at 55 mph or faster, when I take my foot off of the gas to slow down it starts jerking and stalls. Starts right up in park or neutral but as soon as I put into gear (D or R) it stalls, eventually after revving in park, I'm able to shift and it drives okay. I took it to a 76 gas station and they ran the electrical scan with the Chevy computer and showed nothing wrong. Mechanic suggested new spark plug wires and the solenoid replaced which I did, this did not fix the problem. The mechanic also suggests that the ignition module may not be working correctly, would this solve the problem. Any other suggestions? It cost me about $300.00 for the above work and I really can't afford much more unless it's absolutely necessary. Thank you