slips out of overdrive

My 2001 Ford Focus slips out of overdrive gear. I have to press " O/D off" button to keep in drive gear. What can cause this?

I'm experiencing the same problem. 02 w/ 90k miles. Some are saying you need a new transmission, I'm holding out for an electrical quick fix. Check engine light is on; forgot how to pull the codes using the tripometer. Great car!

dont put uour foot to the floor and "slip out"

Are you getting some codes? Somehow, it is related to what I had 3 months ago but my car threw codes. I can't remember what it was but the autozone guy told me that the solenoid is bad. See this thread http://www.automotiveforums.com/vbulletin/showthread.php?t=689062
I had to turn off the OD. Otherwise, I can't drive 40mph.