It's very pronounced while towing, almost unnoticeable when not towing (2,600 lb. travel trailer). Can this be caused by unbalanced tires? Or is there something else I should be looking at? I've recently greased my driveshaft slip joints and u-joints, and couldn't feel any play in any u-joints. I also recently replacing a CV axle, but I thought I'd notice any issues with that at any speed. Thoughts?