1) Defective pump
2) Break in the line coming from the tank - do you have gas line coming out of the top of the tank? I assume yes. If so, the break in the line is above the fuel level.
3) Is there a fuel filter (screen or small sock) on the fuel pickup in the tank? It might be clogged. My 442 had that problem many years ago. What a PITA. Took a long time to find and fix the problem because it ran OK except at WOT. Probably not this per your explanation that "it feels like there is air coming out ...".
3) Other problem