One small note. You are thinking with 1980's type technology.
The problem is not with the alternator, it is with the charging system.
When the engineers designed the electrical system for the GM cars and trucks, they design those systems to use the smallest size wires possible.
They also use the lightest batteries possible - to save weight.
The systems for years are way over loaded with options that does not do much for the actual performance of the vehcle, but is required by law to be there. When you add in the draw of the Power Train Control Module, the Body Control Module, the Radio, Heaters, power windows, lights, running lights, all the options inside of the vehicle. Compounded by cell telephone chargers, lap top computers, and all the perepherial devices.
Some people add's DVD players, monitors, back up camera's, GPS and extra lights and stuff and no matter how large the alternator is - it cannot keep up.
Add to all that, the fact that the government wants the vehicle to get 18 miles to the gallon. The programs in the computers tells the alternator to charge only when the battery shows a discharge, which means that even when you added a larger alternator and a smaller pulley, if the computer does not turn the alternator on, it does not charge. Nor does it charge all the time.
My guess is that the batter life in the near future in the GM trucks is not going to be more then 2 years. For the CAFE standards, it is cheaper to replace the battery, then to pay the toll for the truck not meeting the EPA standards and the CAFE standards for new cars and trucks.
Thank the government for that one.
About the only thing you can do is add the optional battery kit and a second battery. Add a second alternator such as the old style SI 12n20 that came standard in the Caddys and larger GM cars, and isolate that battery from the main battery in the vehicle. You can use the second battery to power all the power options not directly fed by the factory alternator such as lap top computers, DVD players and monitors and stereo's.
