The problem seems to be the main bearings. The oil-pump does NOT create oil pressure. The tolerances between the bearings and journals create the pressure. Had I had the opportunity to respond to this thread sooner I would have suggested a Melling high volume oil pump and increase the oil weight to 20w-50.
If you've already done the pump you know it's only about an hour and a half job. I would still suggest replacing the new pump with the Melling. It increases the volume of oil being pushed into the lower journals and creates pressure ($70) and should give you another 20-30K before you have to replace the bearings. The 20w-50* oil should help close the tolerance in the bearings and create additional pressure.
*20w-50: The "w" in oil refers to Winter. The oil has a thickness of 20 winter 50. Therefore when the engine is started cold as in winter it is a 50 weight oil. The higher the second number the thicker the oil when cold. As the engine warms up it reduces the weight to 20.