Hey Smurf nice team!
First of all, I'd change a little your Garchomp set, an EVs spread of 4 HP / 252 Atk / 252 Spe with the same moveset, with the same nature and with Focus Sash should work better than your current one on your team because on an Offensive team as yours Garchomp doesn't need EVs on HP to have more staying power and it doesn't need Rocky Helmet too, Focus Sash is simple a better choice on Lead Garchomp because it allows you to setup Stealth Rock with more chances than Rocky Helmet and put Stealth Rock is the first goal that an Offensive team should have since it allows to kill opponent's team more easily of course and because it's useful against threats such as Tornadus, Thundurus-T, Dragonite, Salamence and opposing Volcarona too.
I also notice that your team lacks a revenge-killer and it lacks a more bulk Steel-type to check Dragon-types too, so I'd go with Princess Bri and Mr. Green's suggestion to use Choice Scarf Jirachi replacing Volcarona which is a good revenge-kill and a good check to Dragon-types too. An EVs spread of 252 Atk / 4 SpD / 252 Spe with a moveset of Iron Head, U-Turn, Ice Punch and Fire Punch, with Jolly nature and with Choice Scarf of course should work fine on your team.
After that, try Bullet Punch replacing Ice Punch on Lucario, which is useful against Terrakion, Gengar and Choice Scarf Tyranitar which can revenge-kill your current Lucario easily, this is optional, however, if you prefer Ice Punch you can keep it.
As last thing, I suggest you to use Reflect Type replacing Ice Beam on your Starmie which would help you against Tyranitar and Choice Band Scizor which can trap and kill quite easily your Starmie. Reflect Type allows you to avoid Tyranitar and Choice Band Scizor's Pursuit, which can be really useful since Starmie is an important member of your team, it has Rapid Spin, it checks Keldeo and so on, so try it in some battles and see how it works.
Good luck!