I agree, read your manual. Find your engine option, and there should be a tow rating listed.
As for Toyota.com, they say a 2WD SR5 (you didn't say 2 or 4WD) with the 4.0L six is "rated" to 5000lbs. I presume that to be a gross rating: trailer + payload should be <= 5000 lbs.
Sounds about right, my V8 4WD is rated at 7000 lbs. I towed a 4800lb load with it last weekend, about 70 miles round trip, and it performed just fine - but cost me some MPG of course.
If your estimated total load is going to be over 500-750 lbs, I'd definitely follow the general rule of towing in Drive and NOT tow in Overdrive. Your transmission will thank you.