I've read through this...The fuel gauge is a good thing but you did'nt state what the pressure was during the "vaporlock" issue...

Heated lines...OK, but there's alot of vehicles out there with headers and they don't have a vaporlock issue but anything is possible..A factory vapor separator and return line to keep the fuel cycling would be a good thing if you truely believe the vaporlock theory...

Lastely, you've checked the lines leading to the pump for debris...And you've never mentioned how the tank is vented...If it's a later model tank with the 4 lines and divorced vapor catch that itself would be another source for the degrading black rubber...

Which brings me to the last question...Did you verify the vent system is actually working and not creating a vacuum condition under a high load/demand on the fuel pump ???