You can test your shocks quickly. Stand on your bumper on each corner of your car and jump up and down. When you stop, does the truck stop bouncing? If it goes past centering itself, it's time to replace the shocks.
Most shocks should be replaced every 50k miles. They aren't just a comfort feature, they are a safety item. But they shouldn't cause the symptoms you describe here.
Vis-a-vis the brakes:
1) Did you properly break-in the brakes?
2) Do you have high quality rotors or made-in-china? The chinese crap always seems to warp, so I always pay more for made-in-USA.
3) How do you know your rotors aren't warped? You can't see a warped rotor.
4) I've heard of a practice called indexing the rotors. Basically your rotor can go on 5 different ways (or six or eight if you have a HD truck with more lugs), and you measure the runout on the rotor in each position to find out the place with the most even braking feel.
5) Sometimes your pads will "infiltrate" (corrode to) the rotors, especially if the vehicle is parked for a while in the same position. You can turn the rotors to eliminate this, or just replace the rotors. (This happens more with a particular type of pad, but I can't remember whether it is ceramic or organic)
6) If you have a frozen caliper, that could cause uneven wear on the rotor, which would lead to excessive heat on one side of the rotor, and therefore warpage.
Some good thoughts there. Addressing each...
1. Break-in: They've been on there for at least two years, possibly longer. I don't remember if I did anything special for break-in, but probably not.
2. Rotor quality: Don't know. Probably good ones, if I got the work done at the garage where I think I did. I wish I could remember.
3. Rotor warpage: I think if they were warped it would feel different. I'm pretty sure I've had warped rotors on other vehicles before and it felt different.
4. Indexing: I've heard of that too.
5. Pad-rotor infiltration: That sounds possible, if a slight layer of pad is stuck to the rotor (and separated from the pad) it could conceivably cause the symptom.
6. Frozen caliper->warped rotor: As I said about the warpage; and, I expect I'd notice but maybe not.
I'll have to try to look at these things in more detail.
Note that I don't feel it in the pedal, just in the seat.
The wheel bearing sounds like the most plausible explanation so far. I go through wheel bearings faster than anyone I know (regardless of what I'm driving; it's my "to hell with it I'll just hit that pothole" style to blame). In maybe 10-12 wheel bearing failures this truck has had, no two had the same symptom, and considering all the past symptoms this could certainly be a wheel bearing.
I'll have to try to test for it...they often pass the wobble and spindown tests when they're bad, but I'll still try.
Only once have I had a wheel bearing fail on me. It was only like 3 or 4 months after I had put brakes on. I was so upset that I had to take the whole thing apart again that now, when I have new rotors put on my vehicles, I just say screw it, its only a little extra, put new bearings in when its put back together. I've never had one fail since.
My $.02 (and I work in a tires, shocks, suspension, brakes shop) is in line with what everyone else says: shocks or wheel bearing. could be front end (steering) but those are pretty easy to find and are either fine, or not. if it's from the rear, I'd do shocks first. front is a toss-up between shocks and wheel bearings. wheel bearings in a solid axle almost never go bad but the bolt in hubs up front are much easier to replace and go bad much more frequently. as for how often you've replaced them, bolt-in hub bearings, especially on GMs, seem to go bad all the time. though the trucks tend to be overbuilt enough to not be a big issue... meh
1991 Toyota Pickup 22R-E 2.4 I4/5 speed
1990 Toyota Cressida 7M-GE 3.0 I6/5-speed manual
mechanic, carpenter, stagehand, rigger, and know-it-all smartass
"You don't get to judge me for how I fix what you break"
Roll the windows down, turn off the blower and radio and do some hard turns, you should hear some whine, squeal or growling from bearings starting to go out... however, sometimes you have to do a 30 min highway run before they're warm enough to show up.
I've run them until they've been squealing in straight line driving at 50mph, but even then they're usually quiet for 10-15 mins until they warm up, and you could drive round the city at 30mph all day and never hear them.... They may weld up on a 2 hour+ highway drive if they're squealing in a straight line, and heat may damage brake components. I've never driven them to complete failure, but you'll probably smell burning brake fluid before anything falls off, I guess wheels falling off or folding under is what happens when you realise your brakes don't work and try to swerve.
I remember The RoadWarrior..To understand who he was, you have to go back to another time..the world was powered by the black fuel & the desert sprouted great cities..Gone now, swept away..two mighty warrior tribes went to war & touched off a blaze which engulfed them all. Without fuel, they were nothing..thundering machines sputtered & stopped..Only those mobile enough to scavenge, brutal enough to pillage would survive. The gangs took over the highways, ready to wage war for a tank of juice