I agree with G-Benz 100%. If any car I drive isn't charging at 14.5V I start to wonder what's wrong. Keep in mind that even some all oem cars cannot always keep up at idle, with all the accessories and lights on. It sounds to me like you're more knowledgeable and mechanically inclined than you mechanic, I bet you solve it on your own. It sounds to me that your alt is just simply too weak for your car. Maybe a different more powerful alt, or having the rebuild shop boost yours?
I like doing things different and on the cheap, I’d put a high amp unit from a junkyard chevy in there. The boneyard by me charges $18 for an alt.