2002 F350 7.3 5th wheel weight problem
 

I have according to Ford F350 a limit of 12000 lb trailer weight in part to having a auto transmission with 4x4 single rear wheels and 3.73 gear ration. Want to keep my truck. Can it be changed i.e. gear ratio, duel rear wheels etc.

you can change the rear end with a rear end the came out of one with duel wheels but then you have to have one that matches the gear ratio with the front and may have to change the bed to get the rear fenders to gain your desired pulling weight while you're at it don't forget the rear leaf springs. or it might be possible to install overloads on the rear and not change the look of your truck too much

swap out rearend .make it duell