rfrd

I'm having an issue with my 2007 f150. It's a 2wd with the 5.4L engine. I have a fairly steep grade driveway and the truck will not back up it. Seems to work fine in reverse otherwise. It is not the transmission slipping nor the engine "revving up" so to speak. It just does not want to move when it gets to a certain point on the driveway. The problem is only in reverse. The ford dealer has not been able to figure it out so far. They even had the tech try it on my driveway with the diagnostic equipment hooked up and apparently it is showing normal readings. They have apparently contacted their ford hotline about it and have yet to come up with a solution. Has anybody ever had experience or heard of this situation. I somewhat recently bought this truck and suspect the problem was there from the get go, but it took some time before I discovered it. Any help or thoughts would be appreciated.