I tested for opens and shorts, everything as it should be. Measurements between hot and ground, neutral and ground, and neutral and hot all in the 2-4 Meg-ohms ranges. What was interesting though is my shore power cord showed about 110 ohms round-trip resistance with test clips shorting the prongs. With test clips shorting the prongs of the shore-power inlet the resistance measured at interior outlets was 0.0xx ohms(through the breakers and interior wiring). So I brought home the shore power cord and will re-wire the connectors (they're not the molded type, so I can open them and inspect/re-do). Will also clean all prongs and then see what happens when I bring it back to the boat.

Today the boatyard outlet was showing 121v at 60 cycle, I tested it for proper wiring (reversed leads, opens and ground-faults) and it checked OK. Last time I measured voltage at the interior outlets it was 117v but today I measured several different readings between 90v and 101v. I measured voltage on the shore power cord on the end where it connects to the boat and it still showed 120v, but as noted above it had high resistance. At this point I suspect a marginal connection or hot-spot in one of the cord connectors, or possibly on the prongs where it plugs into the boat.... a marginal connection might show a good voltage measurement with the multi-tester but drop when any load is on it. (Power still drops out when I plug in a battery charger, heater or fan.)

If anyone has other thoughts on this I would appreciate input.