1964 Plymouth Valiant Power Issue

Hi everyone,
I'm working on a 1964 Plymouth Valiant v100 and have some type of power issue with it. The car starts and runs nice at idle, but the alternator gauge either stays directly in the center (if no headlights or other power drawing things are on), or goes down into the "not charging" side if the headlights are turned on. The gauge never goes past the center and up into the "charging" side. It currently has a brand new battery, voltage regulator, coil, alternator, and Pertronix kit in the distributor. I've tested for power at the battery, voltage regulator, coil, and alternator and have power in all of those places.The car will run and drive but when accelerating it runs like it's missing and has a lack of power, and if it stalls while on a drive it barely has enough juice to start again. On a similar note, if I leave the car sit in the garage for a couple days it drains the battery. Does anyone have any ideas on what to try? Thanks in advance!