Here's my 2 cents on towing with ANY truck. The closer you tow to the max weight, the shorter the lifespan of your truck. Period. Put all the fancy gizmos you want on it, like oil coolers, fans, and WD hitches, you're still shortening the lifespan.
Toyotas are tough trucks, and will tow pretty much whatever you put behind it, but only for so long. The tow ratings are "max" for a reason, and even then I consider tow ratings to be calculated for "ideal" circumstances (much like MPG's are calculated). Ideal means flat roads.
The tent trailer I tow a few dozen times a year is about half the max tow rating of my 2004 V6 dbl cab. That's about as high as I'm comfortable going on a regular basis. The truck is my daily driver, and I camp mostly in the mountains. I'm hitting 35/40mph on some of the hills as it is, I can't imagine towing anything much heavier on a regular basis. Sure, I could romp on the skinny pedal and go faster, as the truck *can* do it, but then I'm just working everything that much harder, and getting even WORSE mpg.
Eventually, I plan to get a 3rd vehicle that's larger/more powerful than my Taco, and turning the taco into a trail only vehicle. A V8 4Runner maybe, or a Sequoia. Still not planning on a bigger trailer, just making it "easier" to tow my current one.