Sous vide over cooking toughens meat?
Anything you salt will firm up in texture over a period of time. I suspect that since you cooked these with seasonings and then chilled and left them in the fridge before reheating an eating they firmed up a great deal in the fridge. 

If you check out this blind tasting conducted by Dave Arnold at Cooking Issues you'll find some more detailed info about this topic. The gist of it is that for cook-chill-reheat purposes you shouldn't salt the meat before searing. For cook-direct serve meals your just fine doing it that way. 

http://www.cookingissues.com/2011/10/12/to-salt-or-not-to-salt-thats-the-searing-question/