Someone in here struggled with one of the hoses breaking down (maybe the filler hose?) and sending debris into his tank. It was almost the same as the problem you are describing. Do you have a fuel/water filter? At this point I would syphon out ALL of the gas still in the tank. I know you can't see what's going on, but all of your descriptions point to there being some kind of debris or particles in there. I'd probably try to suck out through the filler tube and flush it a few times. Might have to pull the tank to make this happen. It's a pain but not as big of a pain as being stuck.
Former owner of a 1987 Supra Saltare. Current owner of a Malibu 23LSV.