I was just about to make a post concerning this same thing, and then I read your post. I have a 2003 f-150 4.6L with the 4r70w. It has 8,000 miles on it but its all hwy miles. I drive 1,600 miles or more a week. And I have only had the truck for 5 weeks now. But anyway today I was getting on the Interstate and the truck that was in front of me was picking up speed really slow. So I tryed to pass him. At the time I was only running around 25 mph. But when I stomped it down, the tranny shifted down to first I think, and the engine sounded like it was red lining. But the truck was like it was in neutral. Speed actually decreased. When I let off the gas it went back to 2nd gear and done fine. I drove another 200 miles home with no problems. That was the first time I have stomped down on the truck. Like I said all of the miles are Hwy with the cruise set at about 75mph. I havent been to the ford place yet, but I dont really know what to tell them. I have never heard of anything like that happening before.