Re: power drop under load?
Do you have a tach cluster?
I'm guessing, when you come to a stop with the ac on, if it's anything like mine, the rpms drop low then even back out, which could cause the alternator to be spinning too slow to charge.
And as far as when you go to start it, it should be low when you turn the key on, and drop all the way down while starting, then come up once it is running. That gauge tells you whether you are charging or discharging the system, and you aren't charging it till the truck is running.
As long as it doesn't go down and stay down while driving, I wouldn't worry too much about it, and if it does that, the battery idiot light will come on.
I got my Jesus on the dashboard, but the Devil's under my hood!