Engine Mechanical problem
2001 GMC Jimmy 6 cyl Two Wheel Drive Automatic 78000 miles

Vehicle had blown head gaskets - mechanic repaired it, then said that the vehicle was not holding oil pressure and he would have to replace the oil pump. Does this sound right? Is this common?
Replaced the oil pump. Now there is no oil pressure when in idyl. metal in oil.

Not really. The pan simply holds the oil, and closes off the bottom of the engine. Perhaps he said the oil pump? The problem I would worry about is what caused the bad head gaskets? Coolant in the oil is not good for the bearings. If it was driven that way you are likely looking at a rebuild.