I'd started to get an occasional wiggle/oscillation at highway speeds, first noticed it late last summer. Often initiated by hitting a road heave, but once started, the whole truck would do a slow self-sustaining wiggle back and forth, about every second or so. I made sure I wasn't doing it by holding the steering wheel completely still with my leg - just to rule that out. On the plus side, it wasn't really something that would make you lose control, but not good either. I looked over *all* the suspension bushings very carefully. And really didn't see anything. Front suspension is good and tight, lower control arm bushings are all pretty new (one 1.5 years, one this spring) - using OEM. Upper control arms don't wiggle *at all* when turning from lock to lock. On the rear suspension, I pried at all the arms with a long screwdriver - it felt all tight. the only thing I could see was a *tiny* amount of wiggle on the axle end of the Panhard rod, like 1/3rd of an inch or so. No clunking, but able to move side to side a little.
I tried upping the tire pressure some - E rated BFG KO2's in 285/75/16 (33"). That helped a *little*, but once it got started on a wiggle it would still persist until shaken out of it (doing a slow swerve in the lane would do it).
So I got some new bushings for everything in the rear. It's a Sonoran Steel lift kit installed about 5 years ago, with an adjustable Panhard rod. I thought I'd do it in stages on the rear just to satisfy my curiosity about what was wrong. First up - the Panhard rod. The weird thing was that the end that wiggled (drivers side, on the axle) didn't look bad at all. Still seemed pretty firm. Not shelled out or anything. Anyhow, took out the old bushings, wire wheeled the heck out of it, repainted it (rust belt resident here, sigh) and put new bushings in. And test drove it at highway speeds. And? No wiggle. I tried initiating a wiggle, drove over some highway bumps, nothing. Some sharpish twitches at the steering wheel - it would wiggle once or twice in response but straighten right out.
So... apparently even a *TINY* amount of wiggle in a Panhard rod bushing can make the whole truck wiggle at speed.
I also stuck on the cat-back stainless steel Gibson exhaust kit I got in a group buy a few months back. That was a bit of a hassle - the pipes all seemed to have very loose slip fits - and the supplied clamps bottomed out on the threads before the joints tightened up in 2 of the 3 slip joints. And on the one that did at least start to tighten before bottoming out - it ended up stripping the threads before getting tight enough to stop the pipes from sliding apart again. So a bit frustrating. But the SS looks pretty nice, I hope it won't rust.
I also replaced the bushings on one of the rear control arms while the muffler was out. I have silicone bushings for all arms (and two new HD lower control arms) but the daylight was running short, so I just did that passenger upper control arm - made more accessible with the muffler removed. The old bushings looked pretty good still. I tried removing them 'politely' for a little bit - they weren't going to budge. So I resorted to the torch and burned them out. Then cleaned up all the rust (including the hard to remove scaled rust on the inside of the shell), paineted, installed new bushings with grease, reinstalled.
I'll get to the other three arms as soon as the weather is nice again.
