I think they saw a modded jeep and didn't want to deal with it. The tires are new (~5000mi) 265/70-17 General Grabber AT. This is a sporadic issue that was happening on hills and from a stop. Hot weather may have contributed as well (not sure). They were unable to reproduce the problem and pointed to another lifted jeep that had a similar issue.

I will add, that in addition to the better gas mileage, power seems to be better in general since the trans fluid change yesterday...... this is a seat of the pants observation and I have no idea why it would be related, especially given that the old fluid still looked new, so take it for what its worth.