Def look into millennium sport technology supps. I'm an endurance athlete as well and I have to be honest for real hard and long runs I don't like to take anything other than water, BCAA, and electrolytes.
Btw advanced muscle science has BCAA with electrolytes now. Yes I rep them, but it took me a long time to make this happen as I was mixing BCAA wit endurox and hated buying 2 products to make one by mixing them lol. Mst has a lot of good things for endurance though.