Really Strange Electricta/Computer issue, 2005 Dodge

My 2005 Dodge Grand Caravan, <56K miles, while driving LEGALLY in a 35mph zone, suddenly pegged the speedometer to 120 (no change in actual velocity). Tach pegged also and all instrument panel lights lit. This for long enough for the driver (my wife) to notice it, then all back to normal. After driving another 5 miles, parked vehicle for ~60 minutes. I then took over and observed the SAME upon trying to start engine (no revving, either). Turned off ignition, tried again, all normal. Dropped at dealer. Dealer’s service department is baffled. No codes. No recreating the event while test driving. Nothing on their online (STAR?) resources.