There is also an auxiliary filter inside the pump. Have you checked that? It is part # HG-2510090
http://assets.partstree.com/web4/pho...e4c0e/full.png
I have never had to purge any air from a 3k machine yet. Does the service manual tell you to do that?
I'm with the others, if you don't have steering or lift it sounds like something pump related.