Have you towed with this setup yet?
Double check your ratings. You are likely well over both payload and tow rating.
A quick check of the last 7.3 (2003) had 3380 payload and 12,500 tow rating.
With 16k 5th wheel, you should be at around 3200 pin weight at a minimum and could easily be north of 3500lb. Add in 200lb for the hitch weight plus anything else including the husband and you will easily be over the payload.
Not saying people don't do it but he's right about the truck being pretty marginal.
If you have Google Earth (not Google Maps), you can enter a route and then by right clicking, it will show you a profile of the route so you can get an idea of the grades involved. Not perfect but pretty good.
