The computer has nothing to do with those gauges. Go back and check your wiring.

It may be coincidence but perhaps the gauge cluster connector on the back is starting to to get loose. My '92 F350 exhibited the same issue with the voltmeter and temperature gauge. I started to pull the dash to change the meters when I found the connector on the back just about ready to fall out.

Typically if there is an open in the fuel gauge circuit it will read way past Full. If the connector was loose perhaps it may read empty because there is no open length of wire acting as an antenna to pick up induced voltage?