We tow with a V6 4WD Tacoma with the automatic, and really like it. We're getting 16 or 17 MPG with it, and usually drive in 4th gear rather than the overdrive 5th. With a 2" drop drawbar, we're able to run with the trailer level. We're not using a WDH, and we use a Prodigy brake controller.
The truck's rated capacity is 6500#, which seems to me to overstate what I'd be comfortable with. Having said that, we've found the truck is capable of handling all the mountain passes we've driven in Alberta and BC, with just the occasional downshift into third (which has the engine doing 3,000 RPM at 80km/hr).
Fraser & Wendy