Could be the pump has to much clearance. But you do definately have a leak, either gasket, seal, stator ring, cracked drum, piston, or pump. Just take it apart and start checking everything. If the drums all air check good, move to the next item on the list. Be sure the clutches and steels are installed in the drums when put air to them or you may blow a seal. Probably have burned those intermediate clutches already.
