Alright, I need a little advice here. My buddy has a '90 F-250 4x4 with a 460 and E4OD, He does a lot of mild to intermediate towing (3000-7000lbs.) and encountered a problem. He was driving and heard a slight whirring sound which he thought sounded like was coming from around the x-fer case selector, soon after he stopped at a light and began accelerating again and the trans let out a pop or crunch noise and he has major slipping above 2900-3000 rpm. It will shift into all gears ok but slips above that rpm. Also, when not moving, in gear he pushes the OD switch to turn it on and hears a gradual whirring noise that catches up to engine speed and then when disengaged it slows to a stop. Any ideas of where to start looking for a problem. I called a ford dealer and thier trans guy said the Torque Converter could be the culprit but I'm still sketchy. We pulled the pan and the magnet had very small amount of basically normal wear shavings and the fluid was clear and smelled normal. Any ideas?