with the lower sulfer fuels at the gas stations, is it recomended to add an additive to the tank. if so, what one would you advise. i have a 2000 2500 2wheel drive that i use for my every day driver back & forth to work. i also tow a 8500 lb. fifth wheel travel trailer on weekends & holidays. it has 380,000 km. on it. i love driving it!!