We just got back from an (almost) four month stint in YNP. Pulled a 24 foot "toyhauler" Starcraft trailer with a '94 Dodge RAM 250 "commercial" van. It has a small V-8. We have a stablizer package, electric trailer brakes, anti sway control (all added at no cost by dealer - trailer is 2003) Hills slowed us down. WIND was the worst problem, slowed us even more than 9,650 foot "hills". But we were in no hurry and the rig was STABLE. Manufacturer sez it sleeps six but will sleep four adults comfortably. We lived in it for the whole season and are still speaking to each other.
Our fellow workers had much longer rigs but not much more room (?)inside than we. A fellow from Texas had a 40 foot "fifth" wheel which he pulled with a Kenworth single axel tractor. Diesel of course. Air brakes. He bought it for $14,000 and had $6000 worth of modifications done. That is still about half the price of a Dodge RAM quad. He has a 250 gallon fuel tank too. He said the tractor gave him a greater margin of safety for braking. He hauled a full-dress Harley Police Special as well)
A Jeep or any other "consumer" vehicle (like a mini-van) can pull a 14 footer but you won't have a stable outfit and if you are travelling through states like South Dakota, where we experienced winds up to 50 miles an hour, you'll feel like you're towing the Queen Mary.
Buy a good used motor home and PULL the Jeep.