Famous last words. Just to update this thread so others can benefit... I've changed my Rubicon wheels to hub-centric Stealth Custom Series (SCS) K5's (https://www.stealthcustomseries.com/products/jeep) which fit and ride well, but I would not recommend them due to their cheap/uncured powder coating and inflexible warranty. The new K5's enabled me to dump my 2" hub spacers all around (yay!) and generally tightened & improved my ride.So, just as a followup ... the tire balance appears to have been the problem.
After about 4,000 miles on the new wheel/tire combo, my little shake/shimmy (as illustrated earlier in this thread) has returned.
I'm hearing that some have had luck with installation of a beefier track bar (adjustable like https://steersmarts.com/products/yeti-xd-jl-jlu-adjustable-front-track-bar ) and/or sector shaft brace (something like https://www.synergymfg.com/synergy-jeep-jl-jt-front-track-bar-and-sector-shaft-brace.html) ... I'm still running it down.