On a few occasions, although I practiced a piece with a sustained passage in the high register, over and over and even practiced it after having extensively practiced other difficult pieces, when performing I have been unable to control the high register. In the performance, this has been the loud, rousing closing piece, which during rehearsals, I had been able to play well. Generally, I put in an hour to an hour and a half of practice time daily. Sometimes in the few weeks before a performance, I put in an additional brief practice session early in the day ( about another half hour). This doesn't seem to help. I think the loss of control might be due to my tendency to play more intensely during performances than rehearsals and the tension of performing. I also wonder about the effect of intermission and lack of warm up time post intermission. Any advice about how to prevent that from happening?