Easiest thing, I think, would be to check the resistance of the switch. This switch uses a single sensing wire, plus a ground wire. The resistance (from the sense wire to ground) changes depending on which button is pressed (Tow/Haul, ERS+, ERS-, or nothing). If you check it with an ohmmeter, you should see the resistance change as you press each button.
The switch connects to a 6-pin, natural color connector, which I presume is inside the steering column. The switch is between pins 5 and 6 on this connector. If you look into the connector (on the harness) with the latch up, pins 1 and 2 are on the top, and pins 3-6 are the bottom row. Pin 6 is the rightmost pin on the bottom row. Pin 5 is next to it.
You can also check it at the other end of the harness, which is at the TCM. The TCM is located on the firewall, on the passenger side. It has four (4) electrical connectors on the module, but there will be only TWO harnesses connected to it (the middle two connectors just leak electrons onto the ground

). You want the bottom harness. The Tow/Haul-ERS switch goes between pins 19 and 20 on that connector (pin 5 at the switch goes to pin 20, and pin 6 goes to pin 19). Looking into the harness side, with the latch up, the top row of pins is 1-10 (from RIGHT to LEFT). The next row is 11-19, etc. So you'll want to check resistance between the left-most pin in the second row, and the right-most pin in the 3rd row.
With no switch pressed, the resistance should be 18,680 ohms. When the Tow/Haul button is pressed, the resistance should be 4,110 ohms. When ERS+ (upshift) is pressed, it should be 1,650 ohms, and when ERS- (downshift) is pressed, it should be 460 ohms.
You should also check the switch sense wire (pin 20 at the TCM, pin 5 at the switch) to make sure it isn't shorted to ground somewhere. Disconnect both ends of the harness (TCM and switch) and check for infinite resistance to a ground (like the engine block).
Your dealer can also check the switch voltage (as read by the TCM) using a scan tool. Tell them to reference the diagnostics for fault code P0957 to see what the voltage readings should be. Hope this helps....