72 Demon starts bogging sporadically once warm

Sounds like AJ was on the right track, and you may have a venting issue. I am not familiar with the evaporative emissions system on that style of tank, but clearly the hose dumping out fuel is not a good idea. 0 psi fuel pressure obviously is a problem too, can you adjust the regulator? The only other thing I can think of at the moment is the fuel pump is not getting a full 12 volts.