[swimmingly]

I have this same problem and it's very annoying. Most of the time, I only know that I'm somewhere between 3/4 and 1/4 of the tank full because as you said, the gauge only goes up to 3/4 (even on a full tank) and the last time I filled it with the gauge reading 1/4 I only put in 6 gallons and the gas station pump stopped.

Sorry that I can't answer any of the questions but just wanted to let you know that it's probably a common problem since I have it too. If you ever find out what's wrong with it, post what it is.