I realize it has been awhile since this original post but - I experienced a similar situation exactly like what you are describing when I had around 4,000 miles (don't remember exact mileage). My 6.4 seemed to slip gears and then slam into gear going out of my driveway. I thought my wheels may have slipped on sand. I then got a service error on my dash. I turned around and went back into my driveway. I shut off the truck and when I turned it back on the error message was gone. I went back out of the driveway and went less than a mile and started having problems. I drove back to my house and called the Ford Dealer. They had my truck towed in to the dealership. Long story short they wound up installing a new not manufactured (as it should be) transmission. They provided my a rental vehicle while they fixed my 6.4. This was at Brandon Ford in the Tampa, FL area.