On my '06 Tacoma, the tow package option gave me a supplemental oil and transmission cooler (already mentioned) along with the heavy duty OEM battery, a 130-amp alternator, and the 7-pin power connector on the rear bumper. The 2" receiver was rated as a "class 4" tow hitch with the option but I don't recall if that was part of the option or stock.
The brakes and rear suspension were standard, and the suspension was wimpy (to be kind), even without a trailer in tow. I ended up putting Deaver springs on the rear for offroading and I also added air bags for stability and adjusting the ride when I'm towing or have a heavy load in back. The air bags don't increase your load capacity, they just help make it more manageable. I'm happy with the ride both on and off road. IMHO, if you spend a lot of time in the desert, the oil and transmission coolers are worth it even if you never tow anything :ylsmoke: