My front driveshaft is giving me a vibration at about 60mph...it's a 1350 double cardan...when I first was installed no issues...it maybe has 15k on it and I've had the slip rebuilt twice on it and replaced the axle u joints, which reduces some of the vibration. I'm thinking that the double cardan is bad. When I pull it the joint is loose in terms of flexing as in it just flops around when I spin the shaft. It is tight in that if I pull on the joint there is no give in the joints....I've been told the joint should be stiff but moveable....any driveline guys out there? Debating fixing the joint or replacing the shaft all together...tired of throwing good money after bad on this shaft. Thanks in advance!