Your dealer is not right. There have been very little changes in the electric brake system over the years. They MAY have a self adjusting feature or larger magnets, but generally they still work the same. ALL electric brake systems need a GOOD ground, a GOOD power supply & clean tight connections between the truck & trailer plug ins. The most common cause of your situation usually is;
1. Trailer not connected to tow vehicle.
2. Trailer connected with open circuit on brake line.
3. Trailer connector disconnected or corroded.
4. Loss of trailer brake magnet ground.
Try your truck connected to a different trailer. If, you see the trailer connection on your controller is correct, you will get a reading of 6 Gain. This is the ONLY adjustment you have control of on this controller. If you do get the 6 reading, then apply the vehicle/trailer brake & you should see a reading, (after a 3 second delay) of 10, 20, 30. This is the % of power being supplied to your trailer brakes. If you get these results in the above readings then your controller is working as designed.
From what you have told me about your situation, I suspect you have a contact issue between your truck & trailer, & I would first suspect your trailer wiring system. JMHO. Hope this helps you.