Do you know if they replaced both coil assemblies. If this is a northstar there are two of them one in the front and the other in near the firewall. First thing is to check all of the connections in the wire harness. These are quick disconnect assemblies.

 

I also own a 2005 deville and it just started jerking when idoling and going up hills It runs beautifully on the highway. I dont know what to do I really need the cheepest fix possable please help thank you..