I have an 06 taco w/6 speed standard. ~80,000 mi. Towed a 27' jay feather, about 5,000 -5,500 lbs. for about 900 miles into the Bighorn Mountains in Wyoming. About 9 mpg.
An old friend, a WWII vet, said the Army taught him to always keep it in a gear that you could maintain your rpms. I follow that. Push your engine by not downshifting, burn your valves. Ex bro-in-law proved it. No, I'm not crazy. I know it's a lot of weight. Damn fine truck.
I try to keep the motor above 3000 rpm. That's getting it into the max torque and HP range. Less skinny pedal at those RPM's.