Guess I've got a dead cylinder. Now what?

Truck wasn't sounding right, so I took it in for a compression test. Sure enough, Cylinder #1 has 0 PSI, but all the others had 400 psi. What's my next steps?

Rebuild or replace .

First you have to at least figure out what is likely wrong. Could be a blown headgasket, could be a stuck open valve, could be a cracked head, could be a hole in a piston, could be anything. The direction you go really depends on what is wrong. Any other info?

All I really know about the truck is that is had a full go through 2 years ago, and got new injectors. Then it sat almost untouched for 2 years until I showed up to buy it.

I pulled the oil cap and there is zero blow by. It is spitting a little white smoke. I talked with another guy on the way home who said it doesn't sound like it's a blown piston and he thinks it's most likely a stuck valve. Guess I'll pull the valve cover and see if anything looks terribly out of place or stuck open.

Is it spitting thru the intake? First thing I would do is remove the intake. That will give you a bird eye view of the intake valve. The exhaust manifold should be a breeze if the engine was rebuilt 2 years ago. I take original ones apart with hand tools and good sockets. That can be accessed thru the inner fender and you can see that also. But it should e spitting compression out somewhere or tapping loudly. Is it possible a push rod came undone? That would require removal of valve cover. Crank it over see if all is well. Then from that point the head removal and that will tell all after the head is checked and x-rayed for cracks. What ever they do to check heads for cracks. Hope its not a cam lobe. I mean the plot thickens and go can go in deep or discover the issue on the shallow side. Hard to tell from afar. Good Luck. Do it right and pull both heads if one is bad the other deserves the safe treatment at least a through check out at a competent machine shop. New head gaskets and head bolts every time you remove the heads.
Good Luck. Do it right the first time and drive on. Have a Great Day.