I have since taken an AC current reading with my setup (0.4 VAC potential from Chassis to Earth). I am using a 5 prong garden fork as a ground rod. In all cases my measurements are quite solid and not jumping around so whatever is going on appears to not be iffy. Anyway, on the 2.0 AC milliAmp range I have a 100 Ohm shunt resistor and I read a steady 1.5 milliAmps from Chassis to Earth. So, that amount of earth current takes me by suprise and may play a significant role in the "small" picture. I agree the only proper test is to use a heavy current through the ground wire.
Another thing, I am on an acreage 15 miles from the nearest town. The OP could be in the middle of the city for all we know. By this I am implying lots of stray 60 cycle AC earth currents in the OPs neighborhood.
