Septic Scrub may help restore flow to your system. I am not familar with the "sock" you describe. Your description of your system however does suggest that it was not installed with today's design characteristics. Generally today the laterals are laid on stone or select fill, covered with a permeable membrane fabric. This keeps the dirt out while allowing the flow of water. 

I believe that it would be worth it to try Septic Scrub before you encur the expense of replacing the field.