I think something is wrong with your study prep strategy - you are taking classes, working with a private tutor, and using different books yet are not seeing improvements in your weak areas. Working with a private tutor, in particular, should provide an avenue for improvements otherwise I think it's money wasted.

Now about your idea, it is usually a good idea to work on your strengths first until you've leveraged all you possibly can in those areas; at some point your weaknesses will force you to plateau and drag your score down enough to prevent any further gains. You can try to continue building on your strength and see if you score better, but at some point you will have to ask yourself if you hit that plateau at which point you should switch back to working on weaknesses.

P.S. Your time with your tutor should be spent 100% on weaknesses - do not waste precious tutor time on strengths.