1999 F150 towing 6500# 26' travel trailer question

Is 6500 lbs the dry weight or is that GVWR?

It would also be helpful to know your truck's GVWR, front and rear GAWR and curb weight, and what sort of people and cargo load you are intending to have along with you. And how patient you are.

There are hills to climb between Portland and the coast but the elevations are low so that's in your favor.