You might consider spending a portion of your time up in Cooke City or Gardiner. Those areas will offer you better access to Slough Creek and the Lamar drainages. Both of those areas offer very good YCT fishing during that time of year. Cooke City is also a good spot to fish the lakes and creeks in the Beartooths. An area that should have plenty of cold water...

Water wise, things are really heating up right now in Montana. The lower Yellowstone is very warm and we haven't even hit August yet. <sigh>