We have yet to find a margarita as good as this one!
Our Applebee's here in Oly gave me the recipe and there is only one difference from the one you have posted, they listed "3/4 oz simple syrup" to follow the Grand Marnier followed by 1 1/2 oz fresh lime juice etc.. I've tried it with (perfect, just like theirs) and without the simple syrup.

Here is the recipe they gave me:

Build & Shake:
1 1/4 oz Cuervo 1800
1/2 oz Cointreau
1/2 oz Grand Marnier
3/4 oz Simple Syrup
1 1/2 oz Fresh Lime Juice
4 oz sweet and sour

"Simple Syrup" recipe if can't find in stores:
4 Tbsp water and 4 Tbsp superfine sugar into small pan, stir over low heat until sugar dissolves. Bring to a boil, without stirring, for 1-2 minutes. Let cool, then refrigerate for up to 2 weeks.

All else fails, there's corn syrup