If you're getting air in the pipes with the pump off then there is a leak somewhere as Jan suggested. Low pressure indicates either air in the lines which causes reduced pumping or a suction side blockage or air leak. Adding another 20' of pipe should not cause that much added flow resistance. When you get the thing running and stable are there air bubbles coming out of the return jets and is the pump basket full? By stable I mean after it is running for a few minutes after starting. I also assume when you added the extra pipe for the move that the pipe diameter was the same or bigger as was used before. Also remember that it only takes a tiny air leak to mess things up. A long shot but could some crud have been knocked loose like twigs in the pipe or something and tangled in the impeller?
All I can suggest for now.
Al