2010 Ford Fusion Gear Shifting Problems. I need

I was driving my ford for about an hour on the highway and after I got off and stopped at a light my car was still in drive but when i let go of the brake pedal the car started to roll backward. When i pushed the gas the car would rev but not move and no matter what gear i put it in the car wouldn't move. It would also randomly rev very high and the MPH gage would move as if i was driving. I then got my car towed to our local mechanic and he drove it and said he can't see anything wrong with the car. I then took it to a transmission shop and they said they couldn't find anything wrong and no codes were showing up but they can take out the transmission and check every part, but that is going to cost quite a lot.

I have seen videos and comments of people with this kind of problem and they are saying it's not the transmission, it's a Classic valve body (solenoid) failure or the mass air flow sensor. Has anyone had or know what this problem could be?

Those two things will throw codes and turn on the CEL. If the ATF looks clean and is at the correct level I'd just drive it and see if it reoccurs or sets a code.
On many vehicles the "D" or "N" shift indicator light will flash if a transmission code is present.