2015 Pete 389 Parking brake light issue

Picked up my new 389 last week. First load out I stopped about 100 miles up the road to check load. I got back in truck and released parking brake and the parking light stayed lit, speedo not working, engine derated to 1400 rpm and no engine brake. went about 8 mile up the road to Pete dealer and had to wait an hour before they opened. I shut truck off and staarted about every 15 mins and about 45 mins the issue went away. Of course Dealer was to busy to look at it and told me to drive it and see if issue cam back. @ 75 miles later I got to first drop and issue reappeared. Into Irving dealer and again too busy and issue went away. Returned to yard and issue reappeared and to to Austin Pete. They replaced the "transducer" for the parking brake but problem reappeared 45 miles later. It's been at Pete for 3 days now and they don't have a clue.. Any ideas? The brakes are fully releasing when valve is pushed in and I'm assuming that the speedo/engine brake issue is because the computer thinks the truck is parked.