So the Highlander is hauling fine!.My unit is around 3700 lbs, + all the stuff estimated at 500 lbs + 4 passengers...so i think i'm hauling around 4700 lbs.
I'm usually driving on the manual mode with the transmission , mostly on the 4th gear..so the rpm is about 3000 rpm...on the mountains area...i can keep 50-60 mph..but on the 3rd and sometimes the 2nd gear...i prefer more revolution (rpm) than always have many kickdowns from the transmission. When it's ok....i put it back on the 4th. The 5th gear can be an option...but at anytime it will go back to the 4th at any small hill...The 4th is very stable.
The fuel will be around 10 mpg....same as any other pick-up or SUV....with a trailer in the wind...(except a diesel engine)
I don't know exactly my hitch...but it's for my capacity (+ 5000 lbs), not oem-it's after market. I know that i have Huskies torsion bars and anti-sway.
You can't do much speed with the Highlander (60-65 mph is max easy speed to be comfortable), but all i know..is that you do not have to be afraid to wind up the engine...(4000-5000 rpm on hills) you will haul anyting that is under 5000lbs....no problem
Sorry for my poor english, hope it's understandable!
If you have any other question ...ask again!