The O/D indicator light on the dash has never lit up.When it lurched,it did not increase or decrease speed. It happened so fast that it wracked my neck. It happened again twice last night. The first time I was holding steady on the interstate at about 58 mph, and again at about 65 mph ten minutes later. Before I got to my destination, I thought I would see if I could get it to reproduce the vibrations at 35mph. This time it shifted down to 3rd gear and handled very smoothly. Is it possible that it corrected itself? I''m concerned that something is loose that would cause it to lurch and adjust.

now that I think about it... it could be a failing sensor related to throttle or something internal to the transmission. Might be bad contacts on one of the wire harnesses to those sensors (contact cleaner or even WD-40 can fix that - disconnect them, hose them off, reconnect)

It is definitely something that needs to be fixed.