Each GFCI is on a separate circuit with it's own breaker. The GFCI is the first plug on each circuit with 5-6 regular plugs following it. I have had to replace GFCIs before but the problem was always obvious, wouldnt reset, etc. I don't think there is any tool to measure current on the ground available at a reasonable price. When I installed this wiring, I used 12ga wire so I had use the screws on the plugs, So I guess I will have open each box and tighten each one. Looks like a lotta work, but I might solve some future problems.