Unless the fuel and temp gauges are acting identically, the voltage stabilizer will be a red herring. Both have commonly occurring independent reasons to act up.

The most common temperature gauge gremlin is caused by oxidation of the tin contacts on a temperature stabilizer board in the instrument cluster. A whack on the dash above it usually sets it right again for a time.

The fuel gauge can suffer from a sender problem. Around here, that would most likely be rust, but not in Miami or Mexico City.

If the speedometer works but the odometer does not, the likely cause is the gear, but as I am learning lately, not always the only cause.

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Art Benstein near Baltimore