Place the mayonnaise, sour cream, cotija cheese, lime juice, garlic powder, salt , pepper and half the chopped cilantro leaves (reserve the rest of the cilantro for sprinkling over cobs) in a medium bowl. Stir to incorporate the ingredients well. Shuck the corn on the cob. Grill on high for 6 - 8 minutes. Remove from the grill to a plate. Cover with mixture, sprinkle extra cotija cheese over the cobs. Garnish with a sprinkling of remaining cilantro and serve with line slices.