OK, here's the latest on this. about a week ago I had pulled the glass bowl off the fuel pump and cleaned the screen which, since the pump is 30 years old and the bowl had never been off before, immediately started seeping fuel around the old gasket. This morning I shut off the petcock below the tank and ran the truck until it used all the gas in the float bowl, fuel pump and line and died, then I removed the glass bowl on the fuel pump, cleaned everything I could get at again and replaced the old gasket with a new cork one. While I was at it I pulled the seat out and removed the gas gauge sending unit and looked in the tank with a bright flashlight. Darned thing looked new inside, no rust or any crud that I could see. This is the OEM tank too - still has original paint on it. Put it all back together and took the truck on a road trip of about 100 miles. Stopped several times to add gas, which had caused the problem in the past. No issue. Truck ran great. Beats me what I did, but I won't argue with success. I'll obviously be on the lookout for the problem to reoccur, but so far, so good.
