The short of it is with a 5th wheel you run out of payload before you run out of towing capacity. A 17,000# GVW trailer will put 20% or 3,400+/- 300# in the bed of your truck. If have washer/dryer or generator in the trailer it can be even higher. You are NOT in 2500 territory. A 3500 truck will weight about 8,000# add 4,000# for passengers and pin weight and you'll need a truck with a GVWR of 12,000# or higher. GWVR is listed on a tag inside the drivers door. A new 3500 SRW might have a GVWR that high but truck older than 3-4 years will not. Example my 2004 F350 DRW is only a 11,500# GVWR. The new ones I believe are around 14,000# GVWR.
Good luck.