1998 24v

Fuel gauge goes from full to empty every minute or so. Was able to make three trips since it started. Assuming it was the sending unit.

Last two trips:
Started cold in the morning with no problems.
Got fuel. Warm start no problem.
Returned to vehicle, cost start wouldn't turn over.

It took about 5 tries to get it to start and then it works fine.

History immediately prior to issue
After sitting for a few weeks, I noticed that someone had likely siphoned fuel but couldn't get the cap back on (installed bed. Cap binds and is tricky to get in). So its likely that the truck sat for some time with a loose cap. Could the lack of a seal caused pressure to drop and build up on components?

Earlier this year
A gear within the starter broke teeth. Replaced and had no problems.