Just so I understand correctly:
1. The motor "won't run at all" with hose plugged?
2. The truck won't crawl in first gear whether hose is plugged or not?
3. It won't crawl like you think it should after warm up?
4. When was the last time it would crawl like you think it should?
5. You have never said how it runs down the highway after warm up. Stopping at stop signs and acceleration and so on.
I think I would try the hose plugged with air cleaner removed, to see if there is a change in anything. I suspect it will run OK then. This will also let you visually see that choke is opening all the way. It seems like it runs good after warm up like all trucks do after warm up. I don't see any reason to mess with timing. You don't seem to have a very serious problem or headache here. So take it slow and wait for more opinions. I am still worried about the choke, especially with your explanation of how you operate it. If you can't see the butterfly, you do not know if it is open all the way.
If you can hear every cylinder fire, idle too slow. If it idles like a sewing machine, good. Until you get a tach.
