Well I purchased a set a rear Timbrens for my truck. After one week of testing, I decided to return them, here is why. Extremely easy install, that's a given. They absolutely minimized the rock...
As you discovered, the gap unloaded and the amount of compression loaded is the secret to using Timbrens. Did you call them for assistance? They were very helpful to me and provided spacers which really helped my setup, free of charge.