Check list to take a look at. Nothing covering the light sensor ? Truck not in park ? Below is from owners manual.
Daytime Running Lamps
Daytime Running Lamps (DRL) can make it easier
for others to see the front of your vehicle during
the day. DRL can be helpful in many different
driving conditions, but they can be especially helpful
in the short periods after dawn and before sunset.
Fully functional daytime running lamps are required
on all vehicles first sold in Canada.
The DRL system will come on when the following
conditions are met:
The ignition is on,
the exterior lamps control is in AUTO,
the transmission is not in PARK (P), and
the light sensor determines it is daytime.