Task Manager is worthless for real-time CPU monitoring.

Also, CPU usage is a tricky metric. Is there an actual performance problem in your application? If not, measuring CPU activity isn't going to tell you much; it's generally reported as some sort of average over a time interval, so if the interval is long enough the percentage will drop, while if the interval is made too short it will report 100% activity. top can be extremely misleading in this regard.

Unless your program is utilizing 100% of the CPU for extended periods of time, I wouldn't pay any attention to this metric, particularly if the UI is responsive and updates are taking place satisfactorily.