Richard, I think you are wise to pass on that one.
In actuality though, I suspect your 4Runner MAY be powerful enough to "PULL" that trailer, although you'd probably be in 1st gear going up any hill, especially where you live. BUT, i'm pretty sure the tongue weight of that trailer would add so much load to your 4Runner (even with a WDH) that it would overload your axle limits. As an aside, you have to add in the weight of a WDH too - mine is 70#.
I've been very happy pulling my 17ft HiLo with an F150 with the 3.5L Ecoboost engine. I don't think I've ever seen it drop below 4th gear pulling up steep grades (6-7%). However, the trailer has a measured tongue weight of close to 450# (it weighs about 3500# in the normal towing condition), and this means I have to be a bit careful about how much cargo I carry in the truck with my Wife and me aboard.
My truck's "empty" (normal) weight with me and a full tank of gas is about 6500#, but it has a gross weight (axle) limit of only around 7200#. That's the real limitation when you're looking at tow vehicle/trailer combinations.
I've upped my truck's tire load ratings, but I'm right at the axle limits. I suspect there's a margin of safety built in there, and so far, I've not had any problems.
Looking around, I suspect there are a LOT of tow vehicles out there that are running above their load limits.
- Jack