Olpueblo55 said:
(and assured by salesman)
Uh oh, this is never an indication of success...
Partially kidding, but salesman are often most interested in making the sale, and not always in giving you the most accurate, verified information. It sounds like you were confident at the time of purchase though.
I'd say that the Ford towing guide and the Trailer Life Towing Guide are your best / most accurate references, and the number should match between the two.
Trailer Life guides are located here, click on your year (2005) and look up your truck's year/make/model/options for the F-350 series.
That TL guide I referenced has numbers in parentheses for Fifth Wheel tow ratings. For instance, if your 2005 F-350 6.0L diesel truck is Single Rear Wheel (SRW) Crew Cab, the max rated fifth wheel weight is 15,900# for 2WD truck and 15,400# for 4WD truck. Total GCVWR is 23,000#. (That may not be your combo, I just pulled one out of the guide.)
HOWEVER on the F-350 Regular/Super cabs with SRW, or the Crew Cab with DRW, there is something called the "Tow Boss" package that pumps those numbers up considerably. Almost 3000# increases across the board. Tow Boss is denoted with a (b) in the TL guide. So post some more details about wheels and cab in your truck, check out the guide, and you'll know for sure.
That's why you are finding so much variation... there are a lot of options that affect the tow capacities.