the 6700 GVW is a "basic" equipped truck, 8800 is with the "auxillary spring pak" and the GVW ratings were
specifications not 'guidelines', just ask the DOT guy who pulls you over with the portable scales in his truck

and "1 ton" is a
nominal category, not a weight carrying limit
GVW has been discussed here been a number of times, the only thing about the frame that influences it is the presence of long gusset plates rivetted outside the rails from just under the cab to the front hanger of the rear spring ["1.5T" frame becomes a 2 or 3T], otherwise it increases with tire size and addition of the aux spring pak, which because they were optional, could be bolted
Bill