So when you checked the oil the first time it was level and where its supposed to be, then when you got home it was a 1/2 quart past full? I'd say you're getting coolant in there somewhere then adding to the level in the pan. Are you loosing coolant at all?
Other than that, the oil pressure sending unit is probably going bad. It's screwed into the side of the oil filter adapter. You need to get a true mechanical oil pressure gauge on there to be sure what the pressure really is.
And to change the oil pump it's behind the timing cover.
