I recenatly had the auto trans replaced in my '94 full size ford van. I had a trans shop replace the 3 speed auto with an overdrive automatic. I now have a vibration between 50 and 60 mph. If I let it shift from drive to OD between 50 and 60 it instantly starts vibrating. So it seems that the problem would not be the drive shaft or output yoke. Is the torque converter and the flex plate and ring gear supposed to be balanced to each other? When they put in the OD trans they said they put in a new torque converter. I have had it back to the shop and they say there is nothing that they can do about the problem. One employee just says there is no vibration. At the bottom of the converter housing there is an inspection plate. It looks like you can unbolt the converter, rotate the engine until the bolt holes line up again and bolt it in place. Would the converter drop down if unbolted? Would rotating the converter and bolting it in a new place possibly affect the balance? I am thinking that this may increase or reduce the vibration. I don't know waht to do and the trans shop doesn't either. Sign me "all shook up in Phoenix"