I have a Dodge 2500 Turbo Charged Cummins Diesel with a 6 speed automatic transmission and tow gear. You won't even know the horse trailer is back there with a fully loaded 3 horse STEEL trailer, never mind an aluminum one. I also have an older Ford F250 Turbo Charged 7.5L Diesel and it hauls like a champ too. I like the diesel engines because they are much sturdier than gas and as long as you keep oil in them you pretty much can't kill one. The Ford has almost 300,000 miles on it and still runs like a top. The Dodge is new.
I also have trailer brakes on the trailer, I NEVER want to try to stop that whole package with truck brakes alone, I remember those days and that was just way to scarey.