I have a 2007 Ford F-150 FX4 with ~80k miles. I was driving up a slight grade when I lost power to the wheels. It seemed somewhat intermittent, and I pulled off to the side of the road. While tachometer responded to the accelerator, the truck didn't really go anywhere. I put the truck in park and shut it off. I restarted the truck, put it in reverse to angle it toward the road, then put it in drive and drove home without further incident. Prior to this, the truck seems to experience a rough patch shifting gears between 35 mph and 50 mph. I can press the accelerator to get through this speed. The transmission fluid was changed about two months ago.

 

Check the transmission fluid level, and make sure it's not burnt. Scan the OBD2 with a scanner that can read Ford transmission codes.

The roughness at those speeds could be a low grade misfire. If the spark plugs have never been changed, they are overdue.

 

Was the filter changed when the fluid was changed? Filters can plug up.