jliebrec, I know exactly what you are talking about, and it has nothing to do with your GVWR and/or/if your truck is overloaded. The jarring you experienced is a back-and-forth motion, correct? If so, an air-ride hitch won't help, as that only softens the up-and-down movement of the camper.
I have experienced it at one time or another with every one of our units, and we have had several combinatons, some hevily loaded, and others well within limits, like our present unit.
It has always been the road that has caused our problems, and it is the joints in the highway slabs, and the lack of staggering in those joints, that causes the rythmic nature of the jarring. I have pulled over and examined the pavement at times, and have seen ridges as high as two inches on some highways. No wonder the rig is complaining!
The effect does seem to differ from rig to rig, and I think it is the distance between the tires, possibly from the rear tires of the TV to the tires on the camper, or maybe the distance between the camper tires themselves. Either way, there is nothing that can be done, other than to avoid those stretches of bad highway, not always an option.
Think of it this way, if your TV tires are on the downhill side of a ridge, and your camper wheels are on the uphill side of another ridge, that will pull the TV and camper apart. Then reverse the situation a split second later, and the TV and camper are pushed together. Repeat every 1/2 second, bang, bang, bang, bang................. I've been there.
While your truck is definitely loaded, I don't see any reason you should worry about pulling that fifth. Unfortunately, I have never found the cure.
p.s. That is a really nice fifth, as we looked hard at the 26-footers before we went to the 28.