6500 lbs? Must be the earlier model with the 6cyl motor. My 2000 (v8) has a towing capacity of 7100 lbs.
Actually, it's not the towing capacity that you need to worry about, its the tongue weight of the trailer and the payload capacity of the truck.
I pulled a 5600 lb TT with my Tundra that had a tongue weight of almost 800 lbs. Had many problems with the Dual Cam weight distribution hitch and eventually wound up with a Hensly Arrow. I also put air bags on the back of it so when I hauled my ATV, I could keep the truck level. Bags did nothing when pulling my trailer. In addition, I switched out the "P" rated tires for some "LT" tires that were "E" rated.
So yes. Definitely get a WD unit and perferably one with built in sway control. The bars should be rated for MORE than the weight of the trailer tongue....I used 1000 lb bars.
Good luck and I hope this helps
Ron