Need advice if safe for my pickup to pull a heavy 5th wheel

It is not pulling the thing, it is the stopping the thing.

Sooner, rather than later, there will be that split second situation when you will wish that you had a whole lot more truck. Some car will brake suddenly infront of you. You will go into an exit too fast. 16,000lbs of trailer will want to overtake a way too small truck. It won't be pretty.