The pump in our old machine that was going also seemd to "act" normal.. other than what was happening in my above post. We eventually had a tech come out and change the pump, so i'm not mechanically inclined in that area. i wouldn't know how to "test" it. You could try looking up you tube videos maybe? If you have no bubbles or anything like that, then chances are it's not your pump. Have you ever changed the dampers?
I found that as our machine aged, it preferred low head speed over high and higher pass counts to reduce banding. Only bad thing about that is printing times go up significantly.