The Duramax is quiet, smooth and powerful. 0-60 times that will make most cars see your tail lights. The interior of the LTZ is all luxury, void of squeaks and rattles on the roughest roads. The Bose 6 disk is very impressive for a factory system using a center placed subwoofer and 6 speakers. Smoother, stronger and better mileage than the 6.0L 2005 2500HD it replaced.
Sunroof, interior (that's what you see the most), smoothness and of course, power!
Bring back the sunvisor slide outs. The sun can sneak between the visor and the mirror. Open the front fenders to allow for a little larger tires. Don't like the "hippo on rollerskates" look. Make the factory LTZ rims polished. The stock LTZ rims are ugly!