One thing to try is this:
Fill the truck with oil, and loosen the oil filter a couple of turns.
Using a blowgun on an airhose, and a rubber donut (or even your hand) to seal the oil fill hole, force air into the crankcase using the PCV hose or similar. Even if you can only get .5 in there, the pressure will force oil up the pickup, through the pump and out the filter mount.

Good luck!

Last edited by 4runnerpilot; 10/24/09 03:21 AM.
88 Trooper, 2.6 5spd
89 Trooper RS
92 Montero