+1 , Your mains are likely past their service limit and since they get the oil first, you lose oil pressure from there on because of the large bearing to journal clearances. Heavier oil can help a bit, but it sounds like she's due for an rebuild.:(
I'm a Ford guy from way back, but these type of "quality" issues really torque me off. My T-bird had issues with the 4r70w tranny, that was resolved by upgrading some components and changing one or two orifice sizes. Another reason I prefer gears and a clutch!:wtf:
...in my buddies 2001 F250 super duty. It supposedly had a tranny rebuild, but in 2wd shifts late and sometimes goes right into 3rd. Strange thing is, if she is in 4 low, tranny shifts like a champ, nice crisp positive shifts through all gears. I told him it's got to be electronic. Any ideas...