If you have any interest in Dragon Rush, then you can delay Gabite from evolving to get it at level 49 [Garchomp evolves at level 48, and learns it at level 55].. However, you'll have to use a Heart Scale to get Crunch if you do this.
I'd suggest Dragon Claw over Dragon Rush anyhow, but I'm biased against inaccurate attacks.
Your moveset as it is now:
Dragon Rage should be removed, particularly if you intend to level it beyond 50 [where it will be doing more damage than Dragon Rage would to nearly any opponent].
Take Down gets no STAB, Damages Gible and isn't very powerful at that XD
I've found Rock Climb to be more useful than take down, since it has only slightly lower accuracy, a confusion chance, and no recoil damage, and you get HM-use out of it. I'm not recommending Rock Climb, mind XD
Dragon Claw is a good and reliable STAB.. not much more to be said.
Dig is almost always dropped for Earthquake, and for fairly good reason: after the first turn when you dig underground, your opponent will know what's coming next and can easily switch to a flying type to avoid any damage that may have come.. and a good number of Flying-types are faster than Garchomp to boot. I do have a strategy below where you can keep dig, however.
Is your Gabite Adamant, or some other nature? Even if it is Adamant, Fire Blast can be a good option for Garchomp; Takes care of Skarmory and Steelix really quickly, as well as giving you perfect neutral coverage with Dragon Claw.
Two final sets I'd recommend for you:
Garchomp@Life Orb
Naughty Nature [much more likely to be hit by physical attacks]
-Dig
-Rock Slide/Stone Edge
-Fire Blast
-Dragon Claw
Dig underground against an opponent you know you can KO with it, and you've got a rock attack waiting for most flying types that could switch in. This set has a few flaws in it, but can catch a number of people off-guard, as Dig is often viewed as a n00bish choice of an attack. Crobat with Confuse Ray, and a Facading Swellow are probably the largest threats here. Fire Blast is specifically for Skarmory and Bronzong, though you can do more damage to most Steelix with it as well.
The biggest thing to keep in mind with this set: Don't use it on Rock-Types that can Earthquake you, since EQ will do double damage while you're underground. Just use your Dragon Claw on them.
Rock Slide or Stone Edge is your choice; If you plan on solely using the rock attack for KOing lured out flying-types, I'd suggest Rock Slide for being plenty powerful enough and more accurate.. otherwise, I'd actually suggest Stone Edge here.
Also, gave the Life Orb to boost attack power a bit, and since it only activates after an attack hits [won't if they switch into flying when you dig, for instance], you won't lose life unless you've scored a KO most likely. I'd suggest swapping some attack EVs over to defense with the Life Orb on, since Flying-types can often get a first attack in before being KO'd
Garchomp@Salac Berry/Anti-ice berry
Naughty/Lonely Nature
-Dragon Claw
-Earthquake
-Fire Blast
-Swords Dance/Substitute/Sandstorm
A simple set that doesn't really need much explaining:
Earthquake whenever something else isn't super-effective.
Dragon Claw anything resistant/immune to Earthquake.
Fire Blast Skarmory, Steelix and Bronzong.
And the strategic attack..
Swords Dance leaves you open to attack, which could quite likely activate your Salac Berry. Attack and Speed boosted, what more could a Garchomp need?
Substitute will give you status protection from slower pokemon, as well as work you toward activating a Salac Berry, should you be willing to sacrifice HP for speed.
Sandstorm gives an evasion boost, and will slowly eat away opponents. Good if you find your Garchomp being taken down by Focus Sash'd pokemon.. not of much use beyond that though.
Rhyhorn [Lv 49], Marshtomp [Lv 46], or Larvitar [Lv 41] can all be used to breed Earthquake onto a baby Gible, in case you lack the TM.
These are all moves it learnt by itself)
