1997 F0rd F350 with "ERROR.3" on odometer..

[amaccammond]

I have a 1997 F350 4x4 auto tranny. Today it turned 140,000 miles. As I was on my way home, i had the cruise on about 60. Alll of a sudden, it started to accelerate like I stomped on the pedal. I killed the cruise and noticed "ERROR.3" blinking on the odometer alternated with the mileage. I also noticed the OD light blinking. I drove on for a while at 55 and nothing seemed wrong until I would push the pedal and the tranny would want to shift up and down hard, but still gain speed. I pulled over, shut the engine down for a minute, turned the key off and on a few times and the error went away. I drove on got on the highway, put the cruise on 72, and about 5 miles later, wham... Speeds up on its own... ERROR.3 blinks and the whole thing starts over... Drove home at 55 and the truck is now resting in the driveway. Any Ideas???? This is my second '97 F350 with the same set-up and never had anything like this.... I'll try anything on it to avoid the shop$$$ Let me know what you think..