Although a vehicle with a "towing package" may have a higher axle ratio, it is not necessarily what is most important. With newer vehicles having anywhere from 6-9 speeds in the transmission, they can easily tow with a fairly low axle ratio.
Just find a vehicle that is rated to what you need, and in my opinion a 7,000lb rating should do you just fine. Also make sure you have a good brake controller, and trailer sway control would be a plus.
You don't say if you want to go new or used, but a Grand Cherokee can handle up to 7,400 lbs plus has sway control, tranny coolers, and the other items you'll need. You can even have the dealer put in a MOPAR trailer brake controller that is designed to work with the entire system.
http://www.jeep.com/en/grand-cherokee/capability/