The upper Teton has been fishing well with PMDs, Yellow Sallys and caddisflies. You should go early, not only because of the heat but also because the river gets covered up with recreational floaters. They are always on this time of year but the hot weather really brings them out. There are kayaks, canoes, rafts, paddle boards and many other floating devices. I once got ran over by two women in an inflatable couch. Amazingly, the trout continue to feed right through the madness. If you can tolerate the noise and people you can do pretty well, especially during the morning and evening hours.