Bump, Beautiful post, well done CoopWith that many miles on a stock suspension (especially track bar), stock steering (you didn't state, but I will assume) and larger than stock tires, it can be a number of things. Luckily (or not), if you have some tools and mechanical ability, it's easily fixable.
First thing I would do, is to inspect each and every joint on the front suspension and steering. One of the best ways is to have a helper sit behind the drivers wheel and slightly turn the wheel left to right constantly, while you are under the front end looking at and/or feeling each joint/bushing for unwanted/unnatural movement. Two things of note before I go any farther: Engine is OFF and you don't want the wheels to actually turn. All you want here is for the steering system to put some force into the suspension and steering joints.
While the steering wheel is being moved, look at: both track bar bushings (should be absolutely no movement), upper and lower control arm joints/bushings, both tie rod joints and both drag link joints. There will be some movement in the steering joints, this is natural. What you don't want is unnatural movement.....like the tie rods flopping over. I also like to put my fingers on the joint (don't get pinched) as this allows me to feel if there's any unusual grinding, etc. coming from the joints. Replace any part(s) which are bad.
Here's my opinion: Even if the stock track bar checks out, you'll be better off in the long run by just replacing the unit with a stronger aftermarket adjustable one. The stock TB looks beefy, but it is very lightweight and can flex or get trashed bushings, especially with larger/heavier tires. This is true for the stock tie rod and drag link assemblies.....they are pretty lightweight.
Next, check the upper and lower ball joints. You'll need to slightly lift each front tire and support the axle with a jack stand....you don't want the tire too far off the ground. Get a long pry bar and place in under the tire and lift up, checking to see if there is any movement at the 12 o'clock and 6 o'clock positions. I've heard guys have done this with no perceived movement, yet the ball joints were still bad. The stockers have plastic bushings on the inside.....which isn't good. Quality aftermarket ones (Dana Spicer HD and Dynatrac offer them) are all metal.
I just replaced the ball joints on my 18 JL Rubicon (30k miles, with 12k miles on 37's). The stock ball joint ends were very loose, I could easily move the ends around by hand. Whereas the Dana Spicer HD's I installed were much tighter and difficult to manipulate. I could tell an immediate improvement in steering/handling with the new HD ball joints.
If it were my Jeep, I'd suspect track bar and/or ball joints as the most likely culprits, followed by tie rod/drag link ends, and lastly with the control arm bushings.
It is also a good idea to get your tires balanced and aired to the correct level. If anyone tells you it's the steering stabilizer, I'll call BS right now. A properly setup and maintained steering/suspension system can be safely and comfortably run without a stabilizer.
Good luck and let us know what you find.
I’ll second the Trail Grapplers needing very little weight. For a heavy 37” tire, none of mine took over 4oz and they were between 25-40 on the road force balancer.coop gave the comprehensive check list in his reply. And my previous two sets of MTRs/Kevlar needed a bunch of weight to balance so they aren't very true. As a contrast my Nitto Trail Grapplers needed very little weight to balance.
---off-topic---Heck John, I’ll be checking the Nittos out. The only thing that keeps me locked into the G MTRs is that I’ve run them completely flat for a full trail and they held a bead. The one time one broke a bead, I kicked the tire back into shape and it immediately took air.
Sorry, not trying to hijack the thread.