I am driving a 2003 CTD 4x4 with a six speed transmission. I began to notice a vibration about a month ago which has progressively worsened. At first it occurred when I hit a bump or a pot hole but now vibrates particularly bad during deceleration at speeds from 18 - 10 mph. It will definitely vibrate at 30 - 40 mph as well but not as bad and even subsides at greater speeds. Truck is stock everything. Thought perhaps an imbalanced tire or bent wheel but things are getting worse fast and no evidence of uneven wear. I read in other posts about imbalanced drive shafts or yoke problems but I am skeptical because the problem is more pronounced at slower speeds. It doesn't matter whether I am braking or not or if the clutch is engaged. Any thoughts would be great. Thanks