Hi ROC, silkiechicken's worst half here. I wanted to share a bit more info about this shuddering/vibration under braking issue in case someone else experiences this.
It started over a year a go. With light braking, there would be light vibration, under heaving braking, heavy vibration. It was consistent with the speed of the vehicle. Higher speeds meant higher frequency vibrations. My first thought, naturally, was rotors.
As I went to re-torque the wheels, by slightly loosening and then torquing the lugnuts, one of them unscrewed with nearly just the weight of the breaker bar... Torquing the wheels back to spec seemed to help initially, but the vibrations soon returned as they were previously. I don't know if this was the initial cause, but it certainly could not have helped. I'm not the primary driver of this vehicle, so I don't really know how it's been driven.
As silkiechicken said, we tested the axial run-out of the outer surface of the rotor and found it to be < +/- 0.002", which indicated that this was not the cause of vibration. Some folks here had previously speculated that deposits can be burnt into the rotor surface, and that some heavy braking may fix that. So we tried that to no real improvement.
silkiechicken called around to a few auto parts stores to inquire about the cost to resurface the rotors and found one that would do both fronts for $44, which seemed like a reasonable cost for some data. So we gave it a go and what do you know, the vibrations are completely gone. Having this truck brake smoothly has now made it enjoyable to drive again. I couldn't stand it before we fixed this, and I actually think that it made the truck unsafe as it likely increased the stopping distance.
Either way, resurfacing did the trick for us. If anyone else is having this issue, I'd encourage them to consider resurfacing before replacing with aftermarket.
