i have a 94 f150 xl single cab with a 300 i6 and e4od transmission. While driving and at speeds over 40 mph it will drop all gears and act as if i threw it into neutral and after rolling a while it will catch back and continue pulling. i have dropped the transmission down into second when this has happened and i have second gear no question. its just 3rd gear and overdrive

 

Could be something simple like a failing range sensor, just needs to be checked out with a scan tool that can monitor the sensors and computer commands.

 

On a pre-1995 model there is a 99.9% chance that it is a failing range sensor. If it isn't brand new I recommend replacing it with or without data to support the change.