We tow with the truck in my signature - essentially the same drivetrain. Payload is still the Achilles heel here but our TT weighs in at about 6,000 lbs ready to travel. I verify tongue weight with a scale so I do not exceed GVWR.
As for fuel economy we get anywhere from 11 to 12 mpg towing depending on grade and wind. That's an improvement of about 2 mpg over what I was getting towing with our old 5.9 L Dodge van but the Sequoia has way more hp & torque. Solo gas mileage is abysmal in the city but we can eke out nearly 21 mpg on the highway if conditions are right. Good luck & safe travels.