Idle surging, up and down…
 

More often than not, the idle will move up and down a bit when I restart the truck after it has been warmed up and driven. Then, after about a minute or two, it goes away. It’s a straight six, 292, carbureted. It just started doing this recently.
Could it have something to do with the fuel pickup in the tank?
Vacuum leak - if so, why would it go away? Vacuum leaks don’t fix themselves.

Re: Idle surging, up and down…
 

Could be the choke. Not sure if its vacuum operated or manual. If vacuum operated could be normal due to temperature changes from off to start. If you had a vacuum leak you'd most often get a little backfire pop, hissing from leaking line or a high idle. Try locking down choke lever and see if it still has the same problem.

Re: Idle surging, up and down…
 

Choke is mechanical, and pretty sure it’s not moving.

Re: Idle surging, up and down…
 

I replied in General Discussion, moments ago.

Not a vacuum leak. It sounds like it may be spilling a little fuel out of the bowl when parked, and after the engine is running awhile, it clears up. I don't like blaming carburetors for anything, but in this case it may be a suspect since it runs OK the rest of the time.

To add, here- do you run it far enough that the tail pipe turns something other than dark gray? It could be that the float is just a bit too high and it runs OK except for when parked some fuel spills over.