Brake studders, pressure & speed sensitive, NOT rotors

'92 previa, 2wd, 4wdisc, No Abs!
Stutters, shudders & thumps, when when braking. How much depends upon speed/pressure applied. No it is NOT rotors, at least the front ones.
All was fine until my son used it to dodge Katrina. (Wife & I used our '91 Previa) When I bought this van 20 mo's or so ago, I put new pads on all 4 wheels.
I learned at that time to bleed the cargo load sensor at the rear axle last. I have had several Toyota vans for the last 20 yrs, and this is the only one that has this thing in the brake system. I wonder if this is defective or misadjusted could cause my problem?
during this trip of many hundreds of miles, this problem started. Before we left the coast, (house hammered) for Texas, I brought it to a local repair shop. They immediately suspected the ft/ rotors & and turned them. Surprise. Did not cure the problem.
They were covered up w/ other jobs and could not get back to it before we left. It has remained this way since, because we cannot afford to replace parts that do not need replacing. I found finally a shop that gave Me a fair price to replace the Ft. Struts, as they really needed replacing, and told them the story about the brakes. I tried to impress upon them that I wanted them to diagnose the problem and let Me know what it was. Well, guess what? Yes, another knee jerk if it stutters, it's the rotors. They had me get new rotors this time. Each time the pads were also replaced. This time the ft. Bearings (Hub) were also deemed suspect and were replaced, It still stutters. The next obvious suspect are the calipers, but I refuse to spend the $ on ANOTHER poor guess.
Does anyone actually have some USEFUL means to actually diagnose this before more $ are wasted?
At least the shop has yet to charge me, and I'm driving it around trying to see if it goes away, not!
TKS, Pat