still having problems, need advice please

Make a jumper lead with alligator clips. Clip one to the alternator frame and the other to the Neg. battery post. Your initial 5v reading across those is significant.

Your first post indicated that as the engine warmed up, voltage dropped. This tells me that you have a high resistance connection and as current flows through it, resistance goes higher, voltage goes down.

Or the alternator belt is slipping. Sometimes they don't make a noise.