Maybe the light is burnt out. Try running your vin at compnine.com

 

The button at the end of my shifter is tow/haul but I think the o/d kicks on automatically.

 

If you have a 4 speed automatic, you have over-drive 4th gear. Those trucks are known to break the tiny wires that go to the Tow/Haul button. If you hit the button and don't see the Tow/Haul light in the dash come on, that's probably the problem. Search youtube for ideas on repairing.