I have a 99 F250 5.4l 4x4 Super Duty that just all of a sudden stopped going over 30mph. I was traveling down the highway at 70mph and all of a sudden the truck acted as if it were in neutral and started revving up. i let off the gas and the problem stopped. i went to pass someone and it occurred again. I slowed down to 65mph and a couple minutes later it did it again. I wasn't too far from home so i drove it there. By the time i got around the corner I had the truck in second gear to prevent me from going over 25mph. i allowed the truck to rest and then checked the transmission fluid and everything looked good. There was a slight squeak that had just started and appeared to be coming from the drive shaft. I am mechanically inclined but new to working on vehicles.. PLEASE HELP!!