Thinking about it, it does sound ECU related. Have you tried disconnecting the battery for around half an hour? Let the ECU reset and this could possibly cure the problem?
Liam
my focus did this and it was the ECU, used to rev up on it's own as well.
Vehicle speed sensor, plugs into the top of the diff and is made from cheese.
Doesn't the standard Ford radio have a volume control that's linked to vehicle speed, from the same sensor? If the radio volume does odd things at the same time as the other odd things, that's the speed sensor for sure.