I noticed my headlights (low-beams) were not working on my drive home a few nights ago. On this model my DRL's are my low-beams and that isn't working either, high-beams and everything else seems to be working fine.
I've tried replacing the low-beam bulbs, swapped the DRL relay, tried another headlight switch I had. I think the light sensor is working fine since my dash was illuminated the night I noticed my headlights out.

I'm thinking the next step is to check the wiring and ground, anyone else have any suggestions?

 

I'm going to assume your circuit is similar to my 99.

On mine, the DRLs use the filaments of the low-beam bulbs, but in series rather than in parallel when the used as low beams at night.

Could there be some other relays you could check? I don't have my diagrams with me, but my gut tells me there could be at least another relay involved.

 

I had a similar issue with my 02 Sonoma a while ago, and came to the conclusion that it was a grounding issue. The challenge is that these trucks use a very complex circuit for the high/low/DRL systems that switches both the positive and ground wires depending on which light is requested. To further complicate things, there's a few different circuit possibilities depending on what year and model of truck you have.

On my truck, during diagnosis I actually realized that doing the quad beam mod (both high and low beams on when high beams are requested) would fix my problem, so I just did that mod instead of continuing to try and chase the ground issue. On my system that just involved grounding the yellow wire at the driver-side headlight.