[whited44]

Is the air problem while it's running? does it sputter and stall

Or is the air problem only after it sits for a while?

The answer could point in different directions.

If the problem is continuous, then gaskets on filters, the priming pump o rings, or worse case cracks in the incoming fuel line from the tank.

If the problem is only after it sits, you might replace the fuel pump. I think, but not certain, there is a check valve in the pump to prevent the fuel from siphoning back into the tank. First order would be to disconnect incoming line to fuel pump (lift pump, don't know why it's a different name on diesels) to see if the line into the lift pump is full or empty.

The air is a problem after it sits for a while.  Maybe a week or so.  Seems worse in cold weather vs hot.  I'll look into this pump, filters.  I think I have a spare pump.  I'll see if that line is full or empty when I remove it.