I have an older 377 Pete and would get a death wobble at a certain speed.  We changed out a few parts, but didn’t fix it.  A tire guy told me than a belt probably separated on a steer tire.  Took the tires off and ran them to their shop.  One tire was fine, but with the other tire spinning on the machine, you could see where the belt was separated.  Two new steer tires fixed the issue.  Kept the good tire for a spare.