Speaking of the current model Ford F250/350, the physical difference is the F250 has 2" rear blocks between the axle and spring pack, where the F350 has 4" blocks. The F350 comes standard with a rear overload spring. On the F250, the overload spring is optional (camper package). The camper package does not change the GVWR or axle ratings. ALL other components are identical (brakes, axles etc.)
The f350 has a higher GVWR and axle ratings with the 18"+ tires.
It mostly addresses registration fees in some states if the GVWR is over 10k they pay a considerable higher fee.
