I have a Bi-Fuel 2000 C2500 5.7L that's dropping RPM's when idling especially when in gear, and even worse when the AC is on. I feel this when it's running on CNG, but when I run on Gasoline it seems nonexistent. I've replaced the distributor cap and rotor (which were pretty worn) and will be replacing Spark Plugs and Wires here shortly (haven't felt any difference). I'm aware that it could be the camshaft retard offset caused by a worn gear on the distributor. I have not checked that only because I'm afraid of messing the timing up because I don't have software that will read CMP. Other than that, any other ideas of what I can check/clean? I'm not sure if anyone here is familiar with the CNG systems, but it is a Chevy Stock system. Thanks so much, I look forward to any ideas.