No-start Situation - Any Thoughts?

[Zilverado]

Sorry for the long post, but I'll try and get as much detail in as possible...

So I go out this morning to start the truck. It's a little cool at -15 C (5 F), and kinda humid, but that is usually not an issue.

Crank 'er over a few times and she starts up - a little rough, but pretty normal. Let it idle briefly while I scrape the windshield, put it in gear and she stalls immediately. Go to crank again, and she just cranks.... and cranks and cranks and.... Gave it some time and tried again, still just cranking (good strong battery). Not even a hint of a fire. Put the pedal on the floor (thinking she might be flooded), and still nothing - not even a sputter. Look around under the hood a bit (it's dark at 6:00 am here), open the air cleaner to check the carb. Fuel jets are slightly wet, but not like I'd expect after all my pumping.

By now things are getting rushed, so I close the hood and run to the bus stop to get to work...

So, I'm thinking it's a fuel issue - - maybe even as simple as condensation in the lines (did I mention the tank I was using was almost empty), and with the temperatures going up and down here lately.

Since I knew I was running on a low fuel tank, I also tried to switch tanks (I'm pretty sure the other one was full), but the gauge didn't move. I would think the fuel tank switch should work, even with just the ignition switch "on" (truck not running) right? Not sure if this issue is related or not.

Lastly, I wierd thing happened the other day - when I got home after a short drive, I put the truck in "park" on the driveway and I got a bit of a "clunk" from the tranny. I didn't think much of it at the time, but with what happened this morning I was wondering - - since the truck stalled immediately when I put it in gear. But when I tried starting it again, I was back in "park", so I don't think the two are related.

Anyway, I'll take a better look around tonight when I get home, but suggestions of what I should be looking for? Thanks.