Thanks guys. mkirsch, an under-size breaker would make perfect sense for the jack probs... I have tripped that thing dozens of times over the years, so maybe it just had enough.
Bob (CA Traveler) I do have a multimeter, which is how I determined the breaker was bad. That's a good idea to measure power draw while the jacks are in operation though.
Fyi, in the past I did speak to both the dealer and the maker of the jacks (Rieco-Titan) and neither mentioned anything about just using two at a time. In fact, they both said it should be possible to use them all at once (since the remote has an 'all' button). If using just two at once is indeed a limitation, it's a poorly-documented one. I will also post the response from the dealer (about the correct breaker amperage) when I have it.