Steve Schardien

Last Tuesday, I was driving to my dad's house. About 3 miles from his house, my engine started to run really rough. Check engine light started flashing and the traction control light came on. I limped the truck to his house and plugged my code reader in. Cylinder 5 misfire. Truck wouldn't run. I checked the spark plug and wire and everything seemed fine. I have 81,000 miles on the truck and of course the powertrain warranty had expired. I had it towed to the closest GMC dealer in Wilmington, NC. I paid the $160 diagnostic fee. They checked the spark plugs, wires, coils, injectors, and pushrods. Said everything was good. They would have to charge me $1,400 to diagnose further. Meanwhile, I called the dealer where I bought the truck in South Carolina. They said $1,400 to diagnose was ridiculous so I had the truck towed to them. The next day they called and said the truck was fixed. Turned out to be a broken valve spring. Total cost was $400. I picked up the truck and while I was driving, I noticed it seemed sluggish and I was getting a shudder at low RPM's. I swung back by the dealership on my way home. They said to bring it back the following week. (It goes back tomorrow) I'm just wondering if the shudder could be from a fouled spark plug? It happens during light throttle between 1,000 and 1,500 RPM's or right before the transmission downshifts.