Jeff,

Should you find higher pressures as you suspect, I would replace the LPG convertor. As posted before, change the filters just to be safe. There have been issues with the wire harness on the 2.4 GM engines. Makes sure there are no power issues with the coil supply. We have had a number of wires breaking in this location. With your experience, I am sure you have already checked the plugs. There has also been cam lobs that have worn down over time. You can get a GM engine idot light that should plug into a four prong plug either at the engine fuse box or under the floor board on the left side. Hard to reset password without the correct program. Good Luck