According to info provided by Chris King from Toyota of Dallas (trdparts4u.com), my alternator ('98 V6) is a 70 amp, and Scott's alternator ('04 V6) is an 80 amp. I didn't see any 90 amp alts. listed for the '97-'04 Tacomas but that doesn't mean they aren't around. I verified the part # on mine, so I am certain it is the 70 amp. At 135K miles, my 9 year old alternator is still working. However, when running the off-road lights, talking on the VHF radio, listening to the stereo, and running the fridge, I wish I had a higher-output alternator. In my opinion, the stock alternator is acceptable and works okay, (especially if you are going to put some miles on without hi-amp draws, to allow the batteries to recharge) but a 100 amp or higher sure would be nice if you are running high-draw items like 100W lights + toys at night. A higher output unit will also get the battery recovered faster after winching, and hopefully before you get to camp and need all of your reserve to run the fridge, etc.
I am going to be putting new brushes in my alt. soon, and I am thinking about just getting a higher output unit and keeping my OEM as a spare. I am hesitant because my battery solenoid is only rated for 100A.