Usually the tow package option would include an upgraded cooling system...sometimes a larger radiator but definitely an auxillary transmission cooler would be added as part of the tow package.
If your trailer is at or near the maximum capacity of the F150 you should think about upgrading to an F250. Mostly for safety and relaibility. A truck towing at near capacity will show signs of strain and in case of panic stop or aggressive manuevers may not be as controllable as a truck with much higher capacity.