There is a specific Hydraulics forum here on TBN. You may be able to gain some insight by reviewing the posts in that forum. Best wishes. BTW, Welcome aboard.
One of the reasons is that the hyd pump only puts out about 4gpm. Part of the problem could also be because of the way the backhoe is plumbed into the hyd system. Have you cleaned the screen (filter) in the hyd sump
Bill