The restrictions for length and parking in campgrounds is based on RV length. Truck doesn't count.
First, to make this mating of trailer and truck possible, you will need to know the payload numbers (weight of cargo and passengers) from the sticker on the driver's door jamb. Estimated or scaled cargo and passenger weight is deducted from that number and the total is then used to determine maximum tongue weight availability. That 9100 lbs, you can forget about. To really focus the truck advice, list your year, make, model of truck with engine size and final drive ratio.
6000 lbs is going to close to the max you want to pull with that truck, regardless. If this is your first travel trailer and a cross-country trip is being planned, I'd suggest to get something smaller. Tell us how many campers will be going along. If it's only you and one other passenger, a 17' trailer will produce as much fun and be a lot easier to handle for a newbie.
Forget about MPG while travelling with an RV. It will only make you anxious but tallying it and bragging at a campground, "I got 6 MPG coming over the Pass" is permissible.
More info= better advice. Welcome to RVnet Forums.
