Fuel Fluke

ok, my .02 time.... Just read your post and a couple of things come to mind.

1) Fuel sock in your tank is getting clogged.

2) Small air leak in the feed line to either pump. (could be inside tank)

Only 2 things that make any sense from what I have read. The fuel press dropping to 4.5 would mean it's pumping air instead of fuel.