Howdy, I've got an 03' VP 5.0 GXi-E/SX Drive with 120 hrs and at high rpm (WOT-4600 RPM) I just noticed last weekend an occasional popping sound. Loud enough to get my attention and throttle back and I've got a well sound insulated engine compartment. I didn't notice a fluctuation in RPM with the sound and after hearing it a few times I throttled back and took it slower with no more indications. Pulled the plugs and some look like it was maybe running a little hot but nothing that was really obvious. Temps on the guage were normal. I'm running Mid-grade gas and the current tank does have some Lucas Oil fuel treatment/injector cleaner in it. My manual says you can't adjust the timing on the MPI models as it's all computer controlled. So any ideas on what might be the culprit? Could it be the fuel treatment? My best guess was the plugs or timing but if you can't adjust it and the plugs look ok I'm at a loss other than fuel. Any thoughts?