Adding on to Undi's rate, I like the changes he recommended but I think you could still get more out of Garchomp. In BW2, literally every team will be some form of offense so it doesn't need Life Orb to get many KOes, you could try Substitute / Swords Dance / Outrage / Earthquake which is an excellent cleaner along with Magnezone or keep your current set but replace the item with Yache / Haban Berry to make it harder to revenge. I recommend beefing up Garchomp's special defense to the point where it's higher than it's defense so it won't get revenge killed by Genesect with Yache which won't cost you too much power. Some like to lower it's defense IVs to do this but I think that's just a waste of stats.
Hope I helped, good luck.