I have the same issue with my 200o GT
Hey Brother, i had the same problem like two weeks ago, my car is supercharged and i was like what the frig.
I first swapped the filter, that solved the problem for like a week. It then did again on saturday, i pulled off the oil sending unit, and cleaned it out, and then reconnected it, it seems fine now. As for oil you should use 5-30 as the 4.6 motors tolerances are much tighter.............I thought i blew up my motor! It only seems to be doing it after it has been sitting awhile........if this doesn't cure the problem, i will have to put a oil pressure gauge at start up to make sure it is the gauge itself.........the car doesn't wrap or anything it purrs like a kitten.
2000 Mustang GT Vert
Current Mods:18" BBS RK Wheels, UPR Hi Flo Cats; Borla Stingers,Novi 1k with procharger 3 core IC, FMS 42lb injectors, Cobra hat/pumps/tank, pro-m protube, afm f42 cams, 100% stock block/internals, 3.73 gears = 412 rwhp/389 rwtq.