Did a little checking this weekend. So the upper con trol arms are stock unfortunately. I'm not sure how to check and see if the lowers are extended other than measuring the length but i didn't get that involved.
You might want to get to measuring real soon. Considering oem uppers you can be reasonably confident the lowers are not extended as it would throw off the pinion angle quite a bit. Funny that if lowers are extended it could cause 'jitters' as the u-joint loads/unloads. I can't believe problems wouldn't have manifested themselves long before now if that were the case.
The tires appear to be rubbing on both sides of the rear fenders which was a problem with the old wheels and tires. The new ones are marginally smaller so i was hoping that would fix it (very minimal rubbing) but i guess not. This will be a separate thread i guess.
You might think of rewording. Unless excessively worn/rotted bushings then rubbing on both fenders sure sounds like your wheels are just too wide or using the wrong offset??? There is an issue of a small number of frames with control arm mount hole stamped wrong and causing rub on --> one <-- side, but not both. Sometimes a frame can shift on the body causing offest/rub on one side, but again not both.
Would changing the upper control arms and Dick Miller braces solve the problem? How hard are the uppers to change?
If the oem uppers have rotted/badly worn bushings then changeout will of course help. Search will show hints on smart r&r. Having a torch and/or airtools make the job easier. Some guys make a tool with thread rod and plate, and there are tools for rent to ease the job. I did it once using just a BFH and special collet supplied with the extended arms, but it was a bitsh. DM brace will not do much if the wrong wheels already rubbing on both fenders - and if the bushings are still in good shape.
\'96SS SOB: SSRI, Herter Tune, Tri-Y II, , 3000 Edge, F/HO bars, METCO extendeds with CV MMC, Bilsteins, currently Vredestein Ultrac Sessanta (315/35 rear)
\'96FWB BUW-Butt Ugly White: PCMPerformance tune, HomeDepot pipe w/ swissed filter, 1/2 SLP s.s. catback with H- and Flow Super 50s, oem opti rebuilt 3 times, SS Bars, METCO LCAs, Airlift 1000, Monroe SS, PowerTrax No-Slip, and now CTS wheels with +1 rubber. Finally, wait for it... LT-4 knock sensor!