First of all, thanks to everyone who took the time to reply.

As for a "stumble" being mis-described, I had already ruled that out between the corroboration with my son, and the description of the tachometer needle climbing when it was slipping.

So, today I dropped the pan and had a look. The magnet was fuzzier than I would have liked, and the smell of a drain pan full of used ATF is certainly more significant than a dipstick tip's worth.

Even so, I am finding some reason to be encouraged...

The o-ring was present and intact. The filter was not residing detached in the bottom of the pan. However, the fit of the filter neck into the valve body was far from firm. When I compare how the new filter feels (tight and solid) when installed, I can sure see how the old one could have been sucking air once in a while.

This finding has reinstated my wife's willingness to give the van another chance. The plan is to use it more (when gas prices peaked, we took my mother-in-law's econobox out of mothballs for trips that didn't require the van's capacity), and to put me behind the wheel most of the time. Most importantly, we are not bound in a headlong rush for the transmission shop come Monday morning.

We shall see.

Thanks again for all the suggestions