Dip the sliced citrus in a bowl of sugar so they have a light coating. Grill the citrus on medium high heat until they have char marks. Let them rest until they are cool enough to be juiced . Fill your margarita pitcher halfway full of ice, then add the tequila and trip sec. Add the juice to the ice/tequila mixture- by adding it to ice it will help cut the tartness of the citrus. Add the simple syrup in small batches until the proper sweetness is achieved.