[shorod]

Agreed that you should confirm if the bulbs are the issue or not. GM tends to use the high beam filament for the DRLs. If your truck has DRLs, then those filaments are getting a lot of burn time at a reduced voltage, so they could have easily burned out.

When you press the turn signal stalk forward you are turning on the high beams which would turn off the low beams. That's consistent with what you are experiencing. And when you pull back for the "flash to pass" feature, the low beam stays illuminated and the high beam is also powered, which also sounds consistent with what you're experiencing. It sounds like the switch is working correctly (as further indicated by the high beam indicator lighting in the instrument cluster).

-Rod