What are the units for those MAP/MAF readings, and what is the rpm? Get some of the others parameters, like spark advance, KNK, TP, temperatures, injector PW, etc. Did you have a fuel-pressure gauge attached to observe FP during this episode? Is this a return-less fuel system?
Have you tried running with the tank fairly full, but the tank filler-cap loose or off? This problem seems so directly related to the tank level, I am perplexed. Even if there were a leak in fittings/lines on the pump unit (which has been replaced), I would think having all that stuff submerged more would only make things better. I would expect a problem to be worse when the tank level was lower... The one exception is if pressure/vacuum in the tank is abnormal (I would expect only pressure should be there, generally). If a loose cap seems to help, I would suspect the EVAP/purge circus is malfunctioning.
Just kind of guessing now, sorry.