Of course the best solution is the most expensive. It would be a gen3 hemi that drops cylinders and has overdrive for the mileage you would want in a daily driver kind of vehicle. The second best would be a magnum motor probably with a stroker crank to get the power needed. You would again want to take advantage of modern fuel injection and overdrive available for that engine. I would personally stay away from a cummins just because of the weight. Would really strain your suspension etc.