Good report of your experiences!
I also tow with an 05 Tacoma 2.7 reg cab PreRunner SR5. Almost stock. Only changes are 265/70/16 tires, Rostra cruise control and Extang
tonneau cover. And most important, I replaced the rear shocks with Monroes. The factory shocks were awful when towing. Lot's of bounce.
I tow a 2006 Palomino Pony pop up trailer, it weighs about 1600 empty and perhaps 1800-2000 with all my stuff. It has electric brakes (Prodigy controller).
I've towed it from SC to MI a couple of times. A few trips into the mountains, Blue Ridge Parkway, and two trips to the beach. Going camping in Charleston for Thanksgiving and camping in Orlando for Christmas. I figure I've towed about 6000 miles with the Tacoma so far.
I average about 20 mpg towing at 70. There are only two grades through the mountains where I have to drop to 3rd to maintain 55 or 60. Most of the time I can maintain 70 (cruise control on) without any difficulty at all.
I think that 2500 lbs would be about the most I would want to tow with the 2.7. I like to be able to keep up with the traffic...
Glad to hear that I'm not the only one doing this!