Well, we ended up going to Yosemite instead. I decided it was probably foolish to head out on a 1400 mile Baja excursion with my family towing a borrowed 20-year old TT and Brand new 285's, wheel spacers, Deaver AALs, and Bilstein 5100's riding at 3.5" over stock.
I was impressed at how well the Tundra did pulling that 19' TT up some pretty steep grades heading into and around Yosemite. With the Prodigy brake controller the braking was very predictable and smooth. I was even quite proud of my "backing in" ability snugging the trailer into some spots right by the Merced river.
FWIW, the weather was great and the best part was NO MOSQUITOS! :tu: The Merced is definitely running LOW this year though, and I'll bet Ribbon Falls is dry within a month or two, Yosemite Falls not long after that.