Clearly with or without that WDH you are close to spec on all counts. Also clearly the Sequoia can handle it. Toyota is very conservative in calculating ALL the capabilities of the Sequoia. That engine will pull most anything, it's mainly the suspension and axles you have to consider.
Sounds like a nice setup.
I'm planning to get a Sequoia and much smaller trailer for my own use in a couple of years. I've towed with a Sequoia in the past, at about 5000 gross trailer weight, with an Equalizer hitch and the 4.6 L engine that was in the older Sequoias. Went up and down the Bighorns in 3rd at 45 mph, but was still a good tow and a very comfortable vehicle.
