I had the same problem with mine. What spring rates do you have?
Basically, what was happening in my case was the inside of the spring was rubbing the threaded collar. What I did was trim off the excess portion of the threaded collar. Notice the portion of the threaded sleeve that has been wore away.
Trimmed Down Threaded Sleeves
Before:
After:
I enlarge the shaft hole and trimmed the dust covers down to hold up the rubber 'gasket' between the spring and upper mount.
Stock Vs. Modified:
Stock Vs. Modified:
