why won't it go into EV mode?

What is your question?

The hybrid battery is full charge and road speed is about 30 with foot off the accelerator. After highway driving for several miles, EV mode works. If it is parked for an hour or two, then it won't go into EV mode with a full battery until it is driven on the highway for several miles. Check of the engine battery gives 11.89 volts. Local Ford garage tech spent 1.5 hours on it and couldn't find anything wrong!

What makes this problem better or worse?

Worse when first starting out in the morning

How long has your 2011 Ford Fusion had this problem?

A few weeks