Probably since you ran the tank "multiple times" empty and the gross **** at the bottom of the tank clogged the gross **** of a fuel filter and they pressure was pre filter and low on post filter. You should have installed a T between the filter and the tank to see if you were getting fall-off. Either way, completely feasible that the pressure went up after replacing the garbage filter. Also, you could have simply, in addition to loading the equivalent of **** water through it, had a bad filter from the factory anyway.