There was another post about a transmission issue and I searched out an item called "Trans Tune" by Sea Foam. Below is a direct quote from their website, and I put the URL to the page in the 'Trackback' below this text box.
◾“sticking” for a second or two before engaging the next gear
◾engaging the next gear with a jolt
…then your automatic transmission could benefit from a Trans Tune treatment. These symptoms can be caused by varnish and moisture build-up (erratic or sluggish shifting), clogged valve bodies or sticking electric solenoids in the transmission (slow or jolting engagement). Trans Tune can help remedy these conditions.
Since that description "engaging the next gear with a jolt" sounds exactly like my van I'm going to do that first. Then put on another 17K (if the problem doesn't reoccur) until my mileage goes over the 150K mark and get a full service on it. It will certainly be due by then.
I'm thankful for everyone who has contributed to this thread. I'll update when I've got something to report.