*sigh*....Wheel hop question...

you change the shocks?

 

As stated above, change shocks, then put a dial indicator against each wheel with it jacked up off the ground, then rotate wheel to see if anything is out of round. I also had the same problem as you and found it to be an out of round front hub. The problem could also be your tires. Call all the alignment shops you can find and see if any of them do tire truing and balancing.

I can not tolerate a bouncing truck. I would run new tires a few thousand miles, then have them trued. It hurts to see new rubber being cut off, but the feeling of a super smooth ride, and knowing than the now smooth tires will last longer than the before bouncing tires makes up for the loss of rubber. I have had new tires that beat me to death. After truing and speed balancing it was the best riding truck I ever had, Did every truck I owned that way after that.

 

When you did the brakes did you check/tighten the bearings? I don't think the Centrimatic's AND Counteract are a good idea, I've never done it myself but know a guy that tried it and didn't work at all. I'm not familiar with "air-trac" but could be a bushing out somewhere in the rear suspension, but if I was a betting man, I would check the rear slip shaft (on the short driveshaft between the rears) if it is dry(not enough grease,takes a ton) or siezed up it will beat you to death.

 

Do not run balancing beads with Centramatic balancers. They are fighting each other.

I'll bet the airbags are over inflated.

 

I would balance with lead weights. On the inside only if you have aluminum wheels and Centramatics.

Some will tell you to use only balancing beads.

 

I think Stranger has your answer. Jack up your drive axles, spin your tires and see if you have any wheels that are spinning out of round. Very easy and common to have tires slightly mis mounted on rims, and/or rims that are not perfectly centered on the hubs. Out of round wheels will cause your problems and explain why it is only when bobtailing, the trailer weight is enough to hold the truck down and dissipate the shake.