Sorry, I just caught that...You did all of that work and didn't replace the oil pump? The oil pump is the heart of the engine and should be replaced or rebuilt with any engine rebuild... but I digress. The problem with the wrist pin you stated above is often caused by inadequate lubrication i.e. crap in the oil passage, bad oil pump, too thin oil or overheating to the point where things burn the oil off the surface or swell to where there's too little space for the oil to get out of the hole.
Some things we need to know to effectively help you... Was this a problem that started during the first drive after the rebuild, or was it a problem before the rebuild? Did you replace the sending unit before or after you noticed the pressure problem? Have you checked the oil pressure manually as suggested above? Are you using the correct weight oil?
To me, since the oil pressure is good before a drive, it sounds like it could be either crap in the oil pan as I suggested above or a stuck bypass valve in the oil pump.