Sounds like the gas in your tank may have gotten contaminated with diesel fuel. I dont know which is lighter or if the two fuels will mix but my guess is that the oil is lighter than the gas and will separate... particularly in the hot climate... so that when the tank is near empty the oil that floats on the top, will drop and reach the intake of the fuel pump.
If so, and according to your theory, diesel could have entered the fuel system just prior to the low tank being filled with fresh gas. Any remaining oil would then have floated to the top of the tank and away from the fuel intake.
If so then there is the strong possibility that there is still diesel lurking in the tank waiting to strike again!
Solution: Wait till tank is near empty and then drain it.