Can’t go wrong with a 9’ 5wt. Sounds like maybe you are staying above Slide Lake, the river is a bit shallower there. Where it runs thru Grand Teton NP it get fished pretty hard, but the fish are cooperative. August is hopper season and best is to get fly's locally as they will tell you what is on when you are there. Keep your eyes open for moose, especially in the park section. Bear spray is a real good idea. If you are staying where I think you are, they do some real nice trail rides into awesome country. Often see bighorn sheep when we backpack or hike in that area.
