Are you sure you have a receiver on the vehicle capable of accepting a weight distributing hitch? Our 2004 V6 4Runner came with a hitch capable of pulling 5000#, but the receiver was only a small attachment bolted onto the rear frame member. Before towing, we purchased the receiver that normally is installed on the V8 4runner. That receiver bolts onto the rear frame member as well as both main frame rails. Verify that you have the proper receiver.
That being said, we only used the vehicle for 1 season with around 3000 miles of towing before getting a Sequoia. Our trailer was 4500# dry, 28' tongue to tail, and we only packed food, clothes, and water. We have a hensley arrow on the trailer. It would do fine on the highway as long as there were no hills of any kind. Going into the mountains of Colorado, we would always slow down to 35-30 in 2nd gear. One pass that topped out at 11000 feet had us under 15 in first. That was an interstate, so there were no sharp curves and only a 6% grade. The vehicle has gone another 100K since we used it to pull the trailer, so no real damage was done. I used to get 10-12 mpg pulling with it. Never see anywhere near that with the Sequoia, but I can pull the same hill at 55 in 3rd. Being in Phoenix, you will probably be using the AC which will also tax the engine. We never needed the AC in the Colorado mountains.
I would think that with the proper receiver, hitch and light packing, you CAN do it, but will probably be looking to replace it sooner than 3 years. Good luck.