Looking through all these posts, I get the feeling you have a partial blockage from the skimmer to the pump. If you have a main drain, try opening it up to see if that makes any difference. If it improves substantially, then you definitely have some form of blockage. The high vacuum you mention seems to imply that. You say you have to open the filter bleed valve to release the vacuum.

Is there a valve in the skimmer line that is not fully open?

Is the pump overized for the duty?

Have you tried to get a water flow back to the skimmer frm the pump basket housing?

Trying to look at all the things you need to help you fix this.

Pat