And......if you're going to look at "used", I'd sure not limit myself to a 3/4 ton. It's very possible that you can find a 1 ton that's only a year older for the same money or maybe it has another 10k-15k miles on it (which is nothing for a diesel). I would just start looking at all options for diesel.
Getting a 1 ton now would allow you to move up in trailer size, when you're ready to, without having to move up in truck like you're having to do now. And, it's not a matter of "if" you move up......it's a matter of "when". I've read that over and over on many RV and toy hauler forums and thought "not me.....I'm happy with this one" and a year later I was moving up.