Magnum Wagons??

I've got the 3.5 AWD in my 05, approx 130K on it. Don't think I ever got more than 20 mpg. Love the car, excellent for driving in snow, but it has had some issues. Replaced cluster, front sway links (twice), All brakes including e-brake shoes and front rotors changed to drill/slot, Left front drive cv axle. Flex coupler on exhaust pipe, Put a billet replacement in for the little junk plastic shift lock. Biggest complaint is the tailgate won't stay up. Replaced the gas lifts a couple times, but still falls when it is cold.