Truck is used for snow plowing and pulling trailer. With the plow going, strobes, heater, wipers, etc The factory one is starting to strain. Hasn't let me down yet with 81k miles, but I would like to have another one ready to go on the shelf? What is the stock alternator size and what should I go with? Another Motorcraft one? DC Power? What size? Batteries are a couple months old btw.