This has been a good read with plenty of good info and opinions. I have been towing my rig (see sig) for 2 years now with my stock 08 ACC 4.0 w/ tow package. THe last time I put it on the scales it weighed in at just under 4200#, well under the limit of the Taco's pull max.. I have pulled this rig from the DC area to northern Maine, Ohio, Pa, WVA, North and South Carolina and several trips to other states in between. I will be dragging it to northern Vt in a couple of weeks. My point is that my truck and equal-i-zer brand WD hitch set up have worked flawlessly for many miles of both highway and back road pulling. I know I am not near the weigh of the OP's rig and I am glad that I am not. I have always used the 80% rule when hauling with any vehicle over the past 20 years. Do the math, figure out what your MAX weigh will be for your TT and your cargo weigh of the truck(often forgotten) then do not go over more than 80% of the GCVW for you rig ( I beleive teh GCVW for the Taco is around 11,400lbs). This leaves you a little leeway for towing and it can help reduce possibility of litigation in the event you have an incident by not being overloaded. Watch your weight carefully, it adds up fast.
In my experience towing with the Taco and my set up I have had no white knuckle experiences. My set up tracks very well and the adjusted braking system on my rig will stop my loaded rig very efficiently. There has been talk here about the truck weigh to trailer weigh issue and yes the Taco is a light weigh truck but the max trailer to truck ratio is appx. 1.5/1 w/ an unloaded Taco. An F350 with a 18,500lb trailer would be around 1.9/1. Is the F350 safer? or the Taco? All depends on who you ask. As stated in some comments it would seem the F-350 is more dangerous, numbers don't lie. Both are with in their specs.
Tow what you are comfortable with and remember the safety of your family and of those on the road around you. Try it, see how it works and if you need a different set up change up..
WD set up and air bags: When you are setting up you WD system you should have little or no air in the air bags. Your WD hitch should be adjusted to remove most of the sag from the rear and reduce the rise on the front of your TV. If you have the air bags aired when you adjust the rig you will only be reducing the rear sag but not transferring weight to the front to put weight back onto the front wheels and reduce front rise. Airbags are mostly to reduce rear sag when you have a loaded cargo area or using a ball type hitch with no WD.
Here is a pic of my rig set up with my 380# bike in the bed. notice the rig is level. with only about a 1.5" of sag in the rear and .5" of rise in the front.
Your trans: Take care of the trans. Putting a large cooler will help but may not be absolutely necessary. My truck has 42K mile an it and as stated I have been pulling a bit with it. The Toyota trans interval on my 08 is 50K for towing, I believe the new trucks is less. I changed my fluid last week at 42K mile and it was ready for a change if not a little past due. I had a flush and fill. I will do it next in 30K mile.
This is the fluid, it should be a nice red, it is burnt and most of the red is gone.
I asked my trans guy about the stock cooler and thought it was sufficient saying the fluid also goes through the radiator as well. One nice thing about the auto trans in the Taco is that it is overbuild for the truck It is the same trans used on the 4.7L Tundra and is rated for use over 300ft/lbs of torque. Just take care of it.
Be smart, set the rig up correctly, and drive safely. Most of all have fun! If towing is making things hell, consider a different set up. Don't push the envelope.