Re: 2000 ZX3 fuel delivery issues
What you're describing would almost sound like a leak on the sending unit, except that I don't think you'd be burning rich, unless pulling air is causing the regulator to surge. Do you have the means to check gas pressure on the fuel rail?
The only other thing I can think of that could match your issues would be a plugged cat, but that would give you issues regardless of tank level, but it would act up when the cat is warmer.
Prius repellant, just add gas.