Ive had so many problems with the stock 420a alternators and just got a saturn 160amp 1-wire alternator and never had a problem with it. My volts stay at 14-14.3volts all the time. The stock 4g63 alternators arent that great they tend to be pretty weak is what Ive heard.
Also another 1-wire alternator that will bolt up to our motor is the GM alternator(with slight modifications of course).
The best thing about these is you only connect the battery + wire to it and thats all.