The last truck I had in commercial service was a '00 F350 DRW 7.3 PSD. The truck had a 8250 rawr and 4400 FAWR = 12650 lb gvw. This truck pulled my 16k tri axle GN trailer bunked for hauling steel beams used on my job sites.
In this type work we have to declare gross max operational combined weight weight (GCW). The truck was registered at 12650 gvw plus the trailers 16000 GVW = 28650 lb gross combined weight (gcw).
No add ons for more power from the 7.3 as it had to last 150k-175k miles with the least amount of break downs.
Lots of one ton DRW trucks were operated at those weights...making folks a living.
Just pulling a 12k-13k RV ?? As suggested the FTE forums and other Ford diesel webs are a great source for "TOWING" mods to your 7.3/tranny/etc.
There is no GCWR number assigned/stickered/on a placard on any truck.