I've not driven the Durango, so I can't speak to it's quality, may be very nice. Our Jeep had the 6 with the 8 speed tranny, so I'm not really comparing that directly (apples to apples). The ride quality, even if on a similar platform, wasn't anywhere close. The suspension on the Jeep was rough and felt terrible in anything twisty. The GL, even with the extra weight, rides like a dream and feels much more responsive with the air ride.
The Hemi is probably a great motor, with plenty of power, I like it in the trucks. The twin turbo V8 in the GL lacks nothing for me, and it's fun to hear the turbos, lol. It can also be 500hp with only a tune installed at the dealership, though pricey.
The MB upgrades definitely come with MB maintenance costs, but we've had good luck with their warranty service, and a 2year extension for certified used was added.
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