Complex sentence: In 1989, Dr. Jack Graham replaced Weber as Senior Pastor of Prestonwood, by this time considered a "megachurch" due to its rapid expansion, and one of the fastest-growing churches in the United States.
Split into simpler sentences: In 1989, Dr. Jack Graham replaced Weber as Senior Pastor of Prestonwood. By this time, Prestonwood was considered a "megachurch" due to its rapid expansion, but it also became one of the fastest-growing churches in the United States.