2.5 miles with houses and trees in between is a long way. This is one place where more wattage actually comes into play. An antenna upgrade usually does help. Height is might always holds true. But when trees and houses are in the way, power is definitely a factor. You may need more power to penetrate the trees and houses.
Just this Saturday, I proved that to myself by hitting a repeater 10 miles away with 8w that I could not hit with 4w, all else being the same.