2008 F250 SuperDuty with 5.4L and Automatic. When I first start the truck the transmission will start fine, then at about 10 mph will slip into neutral, a few seconds (as many as 45) it will go back into gear and sometimes will do it again. It isn't until I get the wrench light on the dash that it works without ever having a problem again. I have driven 200 miles stop and go without turning it off and never had another transmission shifting problem again. If I turn it off for a second it starts the process over again. I took it to the dealer who says I need a new transmission. That doesn't seem right since it has something to do with the light and it is so consistent once the car is turned on. Help?