[Richard]

When you replace them, look carefully at the relay prongs for any sign of heat. Also look at the mounting blocks that they plug into for any signs of heat or poor connection.

You gave the most important clue of all in your very first problem statement. You said you lost all power to the gauges and back up camera. That means that in either the ignition circuit that turns the ignition relay on or off, the ignition relay or connections, or power cable from the rear to the front kickwell at the passenger seat are the most likely causes. I wouldn't get too concerned about DDEC problems just yet as you track down this problem.