In my state of Pennsylvania you can pretty much register it whatever.
But, you should register it for GVWR. A 4th gen or 2wd 5th gen (both 6900 GVWR) could be registered class 2 which is up to 7000.
A 5th gen 4wd is 7100 GVWR and should be registered a class 3 which is 7001 to ?(atm).
They have been cracking down, and if you haul a trailer often it is becoming in the best interest to register for GCWR which is 13900(3.21) or 17000(3.92) on a 5th gen 4wd.
You should at least do the combined rate of what you pull to be safe.
That said, not many do and the chances are still slim to get caught, but the possibility is growing.
This info from a friends fines and an ongoing discussion about it, and seeing more and more contractors and campers getting pulled over in Pennsylvania.
Just some thoughts, nothing else