My guess is that the engine updates negate the need for a heavy duty radiator or like you said is already incorporated. I see the special edition pkg on the xlt rele is just a way to get a "300a ltd" as it has a lot of the features that were available on that trim with extras that make the pkg more desirable. The low/std to high series for each trim unfortunately blocks you into to certain features without giving you a choice of adding specific items, but I'm sure sales data has a backing to this choice. The platinum trim is now pretty much option free, so that means the price will go up. Clearly, the kr is directly aimed at high country chevy and plat is aimed at denali gmc.