Heat strawberries, sugar and JELL-O just enough to dissolve JELL-O, stirring constantly. Follow box directions for mixing pudding, but use 3 cups of milk. Add sour cream. Fold in three-fourths Cool Whip.
In a 9 1/2-by-13-inch casserole dish, layer wafers, pudding mix, and strawberries. Repeat until all ingredients are used. Top with remaining Cool Whip.