Okay, after I got it all figured out (the ballast emptied, the trailer ball raised), my 4runner tows just fine. It was the collection of things, combined with the soft Toyota suspension, that was the problem, I think.
Here's the rundown of my car's performance:
Was able to tow comfortably at 68-70 mph over level ground (OD off, ECT power on).
Climbing a 12% grade, I had no problem maintaining 45 mph without significant strain on the engine, RPM's were at about 3700 (in 2nd gear, OD off, ECT on).
As for the trailer shimmying, I found something else that would explain: the tire pressure on the right side was at 25 lbs, while the left side was at 45 lbs.
Also, Pete's right about the stopping thing. Wow... is there any way to up the sensitivity of the trailer's braking system?
Overall, towed nearly as well as the Suburban. No problem taking towing with the 4runner for road trips. I'm going to look into getting some rear suspension air bags, though...has anybody installed these? I was looking at the Air Lift "Outback Special (model 1000 bags, with compressor). Anybody have thoughts on these? Seem pretty reasonably priced, around $200. How difficult (or expensive) is the install?
Thanks!
-Cal