As HN* said, sand veil is banned in OU, and the only reason Garchomp was allowed in OU is because of this. so Rough Skin is your only option. Whirlwind > Roar ob Hippowdon, Soundproof, as rare as it is, blocks Roar. you could also use Yawn, but that is really only viable if 1. Stealth Rock is up and 2. your prediction skills are good to spam Yawn by hitting the switch-in with another Yawn. Garchomp is good with a Life Orb set but since Sand Veil can no longer be abused to help set up, I would go with the moceset :
- Swords Dance
so after Swords Dance Life Orb makes Outrage shred non-Steel types the way a blender on those Infomercials shreds dying cats. the only downside is Outrage's confusion plus the +2 Atk boost from Swords Dance is like Garchomp punching itself in the face with Mike Tyson wearing.g brass knuckles......
Karachi looks good, Terrekion is PERFECT, Latios looks good. I would recommend Draco Meteor over Dragon Pulse but I also see why you wouldn't want a -2 SAtk drop on an all-out Special attacker.
BandApe is good, but if you wanted you could always use a Bandzor too. Both have CB U-Turn, but Scizor gets STAB. both get a STAB +1 Priority move Bullet Punch for Scizor and Machine Punch for Infernape. Infernape gets STAB Close Combat, Scizor gets Superpower. Scizor also has Pursuit as an option, Infernape can run Earthquake or Thunder Punch.
overall, looks good, you could also go with Landorus-T...although I think it needs Sand Force over Intimidate. that's all I have to say.
hope this helps :)