50 ~ volts in door/doorframe, intermittently

If the problem is an intermittent interruption of the connection at the ground pin/wire connection in the plug, the solution is to cut the plug off and replace it. As cheap as plugs are, that would be the first thing I tried since you have ruled out the outlet, itself.

http://www.lowes.com/pd_411912-43469-4507_0__?productId=3775769&Ntt=30+amp+plug&pl=1&currentURL=%3FNtt%3D30%2Bamp%2Bplug&facetInfo=

If that is the problem, testing it for continuity won't mean anything, because it may be making contact when you test, but lose contact later.