Air in fuel issue

Update

The mechanic has determined the same thing I have and recommends a new tank. I priced it out, peterbilt says I need a new tank "assembly" - for a cool $5500. There is a local tank making place will make me a new tank for about $1900 and I figure call it 2500 by the time I pay the mechanic and fittings etc. I have one last idea to try before I go that route. Make my own fittings, replace vent with homemade setup, see what happens. Leave current supply just barely cracked as a makeshift vent. Or, perhaps someone can tell me if my fuel caps are vented or not. I can take pictures and send them early next week (shop is half hour away).

 

Venting is not the problem. The problem is both pickup and return pipes inside the tank are allowing air in at the same fuel level leading me to believe they are welded together and over time cracked. I have anti siphon welded in from the factory not removable making it impossible to see inside the tank. The factory welded the threads of the current pickup and return pipes where they connect at the top. I did every test I could think of even replaced the vents on both and tests with fuel caps totally off so it can't be a pressure issue.

 

It reads off the right tank, don't believe there is an unused hole to move fuel level sending unit to the left. I will check when I go pick it up.