If your on-camera flash isn't overheating, why would the remote flashes have that problem. If you're always firing your on-camera flash, I would venture to guess that one is putting out more power than your remotes set at 1/32 or 1/64. Do you think it might be a range problem -- 100ft isn't all that far.
Since it's part of the discussion, what do most of you set your speed lights at when flying them as remotes on stands? It sounds like jaayres20 is using the eTTL function with ratios...how is that working out for you? Is that giving you better light than setting the remotes on low manual power?