I recently had the heads re-worked and installed. While driving at normal rpms the truck is great, but when at a red light or stop sign the rpms drop drastically and starts a rough idle and also the valves start clattering. As long as I keep my foot on the gas it levels off and is good? I'm wondering also about the timing? No codes are being shown on the computer. Can I take it to a dealership and have them do some sort of calibration?