high gear
The highest, fastest, or most efficient level. We've expanded our development team and are in high gear working on our next project. Construction is in high gear all around the city as it prepares for the upcoming Olympics.
high gear
A state of maximum activity, energy, or force. For example, His mind was in high gear as he studied for the medical exam, or The political campaign is finally moving into high gear. This expression alludes to the high gear of an engine transmission, used at the fastest speeds.