Yes it is. Try higher than 10 perhaps. Tire will likely overheat if driven at high speed for too long at that low a pressure:
- http://www.4crawler.com/Diesel/Tires...roperInflation

I recall running my Swampers down at 15 psi or lower quite often on the road, between trails. I recall they were rated at something like 2500 lbs/tire load rating @ 30 psi, so 15 psi is in the ball park for a 4000-5000 lb. 4Runner.

 

new discovery! i have a "death wobble zone" between 30 and 35mph. i was late comming back from my lunch break today and decided to gun it and got going pretty fast w/o a wobble

 

Yep, that is normal. Mine was about the same speed. If I could accelerate through that zone without hitting any bumps in the road, it was fine. If I hit a bump and got the wheels going, had to slow down or hit the brakes to settle it down.

 

haha yuuuup im going to make use of my detroit locker to gas it around corners to try and wear the rear tires evenly and then rotate them to the front and hopefully that will cure it. at least i know now that i can go faster haha and dont feel like im driving a tractor