UDo's Choice is awesome, the best source for all your EFA needs, or in other words essential Fatty Acids, ie Omega 3's 6's. Here is a link. This stuff is no joke, seems to make me just feel better, plus excellant for all on the CKD's. Here is a link off the Manu's Website. Im not sure of all the claims but it has seemed to helped my endurance a smidge, but again I only take 1 tablespoon once a day for 2 weeks, you are supposed to take like 1 tbsp for every 50lbs, but its expensive.
You can't get it at GNC, but most decent health food stores have em.