1996 f250 vibration from 55-60 Hi guys I’m new to this forum. Thank you for any help up front. I have a 1996 f250 extended cab short bed powerstroke. It started life out as an auto 2wd. I have since converted it to a 4x4 manual(zf-5). Front axle is a Dana 60 with rsk. Before the swap I had no vibration. To start I had a one piece rear drive shaft made with a two joint system. My working angles were around 6 degees. Seemed like a no brained that that was the vibration problem. I had a new drive shaft made that was a double carder joint up front and the shaft was balanced when made. I put 5 degree tapered blocks I rear to line rear yoke up with the drive shaft. After all that the vibration is still there. My new trans mount seemed two be a little week and allowed to much movement. I then got a trans mount from auto fab with prolly bushings and the vibration is still there. As Info it vibrates with rear tires off and it on jack stands at 55-60 mph. On jack stands the vibration will go away with rear drive shaft off. It seems odd that it would do it with two different drive shaft setups with both of them being balanced. With the truck on jack stands the vibration looks/feels to be consntrated at the transfercase/transition. Truck has new clutch with sm fly wheel also. Iv been over and over what I thought it could be and I’m left scratching my head. Every time I think I’ll have it fixed it’s not fixed. Only thing I haven’t inspected much is motor mounts. They were new in 2015. Only thing that seemed to help was when I had the old trans mount on there I suspected that was the prob so to test it I wrapped a strap around trans to the cross member and tightened it down. This seemed to help and almost make the vibration go away. So I replaced mount with a better one and the vibration is still there exactly the same.( vibration is the from 55-60mph cursing, speeding up, all gears at the speed, nutrel, clutch in, and slowing down, vibration starts at 55 and goes away shortly after 60mph.) thank you for any help I’m at a lost at this point.