Well your on the right track by thinking about hooking up a known good mechanical gauge and watch that along with the electrical one (if you can hook both of them up it would give you a definite answer).
Try that first. At least you'll know for sure what your problem is.... bad gauge or
oil pressure problem. And if you go so far as to drop the pan to look at the pick-up, I'd change the pump at that time anyway..... isn't a whole lot more stuff in there that would cause a loss of pressure like your reporting.