I have a 1977 F250 Hiboy which i am having a driveline vibration issue. The vib occurs at 50-60 mph and feels just like a tight or rusted ujoint. I also have a launch shudder from a dead stop to about 10-15 mph. The launch shudder and speed vibration developed at the same time. A year ago i did a 360 to 460 swap. I used L&L conversion engine mounts and towers. I also swaped C6 trannys at the same time ( bell housing compatability ) At that time, no new vibrations developed. This spring, I replaced the rear leaf springs (had 4 broke on one side due to 30+ years of use ) I selected stock height, stock replacment springs and also replaced shackles and rear hangers at the same time. Immediately after the spring replacement, the vibration developed. I figured fresh springs increased the ride height ( I noticed a good 4" increase at the bumper, but again had many busted springs to start) So even after 5 months, the springs have settled a bit, but vibration is still there. I finally measured my engine, t-case, and pinion angles and measured as follows: Engine 3.5 degrees, center shaft 10.5 deg., t-case 6 deg., rear shaft 12.5 deg, and rear pinion angle 8.5 deg. As I mentioned before, the motor mounts were swapped with L&L kits and I never measured the old motor angle. The T-case is the only component which has not been modified in any form. From what I see, I think that I need to shim the rear axle to match the t-case and try to adjust the motor to match the t-case. The working angles of the joints seem too steep to me. Any suggestions as to where to start?