Hmm, the machines usually will test voltage at rated current. So if they are good then something on the car isn't. I would check out the basic power wiring layout. Make sure feeds to the fuse box and dash are all good and clean. They come from the power distribution on the inner left fender. that gets power from a smaller red wire from the positive on the battery. Also the grounding path between engine, body, and battery needs to have a good low resistance path.
When you connect the alternator are you connecting the small red wire to D+? there should be a case ground to the bracket on the engine. The big red goes to B+. some alternators have both a D+, and a D- on the back. D+ is the proper connection for the small red wire. Keep at it, sometimes these electrical issues are more than one bad connection or problem.