Tyranitar - The EV spread is wrong. seeing as you get a Special Defense boost from the Sand, and having Curse, I would suggest 252 HP/76 Special Defense/180 Defense with a Careful nature.
Garchomp - Again, but not the right Item paired with the nature. I would Suggest Switching the nature to a Adamant one, seeing that you have a Choice Scarf, and thus you'll get a great Attack stat with an amazing Speed, thanks to the Choice Scarf.
Excadrill - Wrong moveset. go with:
Trait: Sand Rush
EVs: 252 Speed/252 Attack/4 HP
Shuckle - Good moveset, but I would suggest:
EVs: 252 HP/252 Special Defense/4 Defense
Gigalith - Good moveset. Nothing to change.