Fuel pressure regulator going bad maybe allowing to much fuel in? I'd think a vacuum leak anywhere in your system would cause a +* LTFT since there is unmetered air entering you system casing it to run lean making the PCM add fuel, but if there's a vacuum leak around your FPR it could be showing less vacuum causing it to run rich. (thinking out loud seeing that since you lose vacuum once throttle is applied and more fuel is added) You are having rich conditions causing the PCM to remove fuel...
I could be complete wrong, I hope others chime in, but I'd check your fuel pressure at the rail to see what you are getting. I forgot if the Schrader valve is located pre or post FPR though, I think post. If you have proper pressure, could be an injector stuck open?
