I have a 2011 F-350 Dually w/6.7 liter diesel. It pulls large 5th wheel. Truck has 91,000 miles and I bought it new. Recently a "trailer disconnect" msg routinely appears on dash. only for a few seconds. then "trailer connected" comes on. On a recent trip of 600 miles it did this 200 times. Have checked power cord pins which are good. Brakes lights and turn signals work when disconnect message is up. Truck has a factory tow package. Have checked power cord harness at 5th wheel hitch. seem ok. where should i look next?