I have a 98 1 ton chev that I dropped a Cummins in and there's air getting in the fuel from the in tank fuel pump and I can't figure out how. I can take the line and put it in a can of fuel and it runs just fine. Has anyone had a similar problem?

 

Hole in the sending unit above the level of fuel in the tank likely.
Check around any welds on the dip tube,and or close one end of the tube and put it in some soapy water and apply low pressure air to the open end and locate/repair where it bubbles.