The pumps use oil pressure from the engine to feed a "seal" which prevents fuel leaking intro the engine via the pump. Eventually the neoprene seals under the pump elements fail and oil finds it's way to the governor via the rear bearing. Once the governor gets over full you will experience problems with sluggish acceleration as the governor weights cannot swing out correctly . The oil acts as a brake . because the governor wont work you don't get enough fuel under load. Hence your missing going up a hill etc.
drain the pump by sucking out the old oil with a turkey baster through the dip stick ,or if you want too, remove the large nut on the rear of the pump and drain it out through there. In your case I would use ATF, then go for a drive and see how the car behaves. If that fixes your running problem but the oil then rises over a few days of driving ,you might consider getting a pump core and getting it rebuilt,then swap it in later .