Check the pins on the leaf springs which locate them on the axle - mine had one of these snap a few years back, and the result was the crabbing thing. The u-bolts were tight enough to stop the axle from sliding right up the leaf spring, but still allowed enough movement to cause trouble.
I replaced both leaf springs and all the u-bolts for new ones, and never had the problem again.
Don't give up on the KE-55 - you were right, they are great!