High altitude pizza crust - how to adjust yeast?
Sugar fermentation occurs more quickly at high altitude so you need to cut back on the time that you're allowing the dough to rise.  

Salt controls the action of the yeast so you might be able to increase it slightly since you're talking about pizza crust and not a sweet yeast dough.

Are you using all-purpose flour?  If so, try bread flour.  The higher gluten content of bread flour typically requires a longer amount of time for rising due to the extra gluten that needs to stretch and expand.  Additionally, it will be a stronger dough even when it is expanded.