Doing about 75 MPH on the freeway this morning, something happened with the '05 Envoy. All the warning lights came on, all gauges dropped the 0 and I think the engine died momentarily and revved back up again. As I was pulling over, the lights went away and all gauges went back to normal - except the oil pressure and coolant temperature gauge. Oil pressure was pegged at 550 kPa (80 PSI) and coolant temperature was showing 110Â°C (230Â°F) - even though it read 202Â°F on my ScanGauge-II. Killed the ignition and restarted it, all gauges were normal except oil pressure and coolant temperature. Worthy of note, the positive battery terminal bolt needed replacement, which I didn't get to yet and I had the infamous starting problem I posted about earlier. When you kill the ignition, oil pressure and coolant temperature do not revert back to 0 like the rest of the gauges, they're pegged in the center of the gauge. Does this sound like a stepper motor issue, triggered by a poor battery connection or am I looking at something else? Thanks!