Clunk in my F250 when accelleating from a dead stop.

I agree that it may be the slip yoke is binding and causing your clunk. Easy fix, some companies used a specially formulated grease for longer service intervals.

I would also check the motor mounts as the slip yoke usually makes itself known under light throttle from a stop, or even pulling up to a stop. What you are describing takes a heavy throttle and is worsened by a turn. Check your engine and transmission mounts under load with an experienced helper that knows how to check the mounts.