I may well not be leaning correctly yet, as a lot of the flying I have done has been below 3000ft, and I would not lean below that level.
I'd read up on this if I were you, you can lean at any altitude, the issue is power setting and I'd be amazed if you were above 65% in the cruise. I assume it's carburettor? I'm sure the handbook will encourage leaning in the cruise. It'll save you a good few bob on fuel AND it's better for the engine