On a 1994 F150 4x4 with 5.0 & 4 spd. automatic, (4R100 trans), when cruising between 50 - 60 miles per hour, the truck keeps shifting up & down, up & down, will not cruise steady. It has 72,000 miles on it & it has always done this. This can't be normal? Anybody else experience this? Can anything be done about this? All your thoughts are welcome & appreciated!

 

Sounds like your torque converter is shot and won't lock up.