I had same type of problem, along with a front end that didn't seem to want to stop pushing until the front shocks were set to nearly the full amount of preload available, which surely didn't help the ride any. I found that the front rear suspension spring had been set too stiff from the factory. There is a snap ring under the lower spring cup that can be moved. Mine was set in the 4th or 5th grove from the bottom, and I moved it to the second. When I rechecked my sag it had changed from 6 inches to 10! I reset the rear spring to bring it back to 6 inches and it seems much better. I now need to refigure where the front suspension springs need to be to bring them into the same range as the rear end. Be sure to remove the tension on that front spring by disconnecting the limiter strap
before you try adjusting that front spring, it has a bunch of pressure on it otherwise.