To go to every state you would be doing some long crazy zig zagging across the country. You would also be spending a good deal of those 6 weeks in the car not seeing much other than driving by. You can definitely see lots of the US in 6 weeks but you ll want to pick a few states, don t try to see all 50 (or even the 48 contiguous). November/December in the northern US will be chilly to cold with the potential for lots (or no) snow. Driving can be a bit more difficult. Not the best circumstances to start driving on the opposite side of the road.NYC for Christmas is definitely a great choice! We do a pretty darn good job of it in my opinion.However your plans work out, have a great trip!
I doubt you can get to every state in six weeks. Read Bill Bryson s book Note from a small Island where he failed to visit everywhere in England.