Sounds like you have a vehicle speed sensor concern or a psom concern. I have seen both of these items fail & have the exact same symptoms that you are describing.
The easiest & cheapest way is to replace the vehicle speed sensor located on top of the rear differential housing, if that does not take care of it, more than likely you have an internal instrument cluster concern (psom) that is sending an erronious vehicle speed signal to the pcm & causing it to cut off fuel.
The pcm goes into fuel cut mode once it sees a speed signal of over 97 mph, which with what you are describing of your concern & your speedometer going nuts, this is your problem.
Hope this helps, I recommend using a factory Ford rear axle speed sensor & not a cheapo aftermarket part, I have chased too many "ghosts" over the years by using cheap aftermarket electronic parts.
Thanks & have a great day, Shawn.
Ford Senior Master Technician
20+ years Ford, Lincoln, Mercury experience, Senior Master Ford Tech, ASE Re-Certified Master Tech