Like Balzaccom says...
For longer trips you're going to almost inevitably be dealing with higher elevations. Something to get you going is maybe to either try to add a couple days upfront if you can change your plane tickets, or maybe take a couple out of that 8 for some time to acclimate. It's also pretty hot in August, and heat and altitude will mess you up and possibly end your whole trip within hours if you don't give yourself the time to do it as best you can. Even with only 6 days, you're going to spend a good part of your time at or above 9000-10000 ft so it's sort of a big deal.
Also, both permit-wise and massive crowd-wise, in August, trail entry, or even simply dealing with Yosemite Valley itself, sucks a lot. Tuolumne can get just as crazy. August also means permits can be tough to come by for a lot of popular trails everywhere in the park. Be flexible.
40% of all permits are walk-up for any trailhead, but if you see that they're booked solid in reservations, permits are probably going to go fast on those walk-ups, too.
Use this for reference:
https://www.nps.gov/yose/planyourvisit/ ... lheads.pdf