Reading the OP, it appears that both the fuel and temperature gauges are affected, so little point in pursuing senders etc as both are unlikely to fail at the same time.
Last year I experienced similar whilst in a traffic jam, with only fuel and temp gauges affected.. Switched off and started again and it was fine. Have since done a few 1000 miles and it hasn't reappeared. So I think it must be electrical/ECU based. First port of call has to be dashboard connections and instrument voltage regulator (unless that is also ecu controlled)
