If you are planning to tow horses around often, you'll be better off in the long run to get at least a 3/4 ton truck. I think that you'll find a V8 engine to be just as economical in a work truck as a 6 cylinder is. And as a general rule, V8's give less trouble.
A heavier truck is also much safer to tow with than the mid-sized models.
Having said all that......
I currently drive a restored 1966 Chevy 1/2 Ton.
It don't have all the comfort do-dads that the newer trucks have but they made trucks heavier and stronger back then.
It allways starts, it allways gets me to where I'm going and it has done everything that I've asked of it.