'83 W123 battery drain problem

[lobu]

If I don't get my engine up to 3krpm a some point th alternator will not be in charg mode.

I had replaced the battery, alternator (and yes even that diode thing in the back) a year ago thinking that was the issue but no dice.
I put a volt meter to the fuse box. Everything was normal meaning(just a tiny drain on one fuse going to the clock).

If I drive around town and don't get the engine at high revs, the alternator will act as a draining device and I'm toast.

When I give the engine a good rev past 3krpm the lights, become energized and the alternator is in charge mode. I know this because I had to jump my car, once started I reved the engine to a high rpm. I drove for like half hour and I was able to restart my engine later.


So what the heck is going on?