At idle and under 2k rpm’s it’s fine, blows cold. Once I take it over 3k it shuts off and comes on, even sounds like the clutch grinds, back and forth. I replaced the compressor and filter and drier last summer. I think I also have an alternator problem. Just old. My lights dim when under power. Could it be the same problem? Lack of power to ac compressor?

If you know the alternator is bad replace it before worrying about anything else.

Agreed