We found one dictionary that defines the word to shift into high gear:

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1. to shift into high gear: Collins English Dictionary

▸ Words similar to to shift into high gear ▸ Usage examples for to shift into high gear ▸ Idioms related to to shift into high gear ▸ Wikipedia articles (New!) ▸ Words that often appear near to shift into high gear ▸ Rhymes of to shift into high gear ▸ Invented words related to to shift into high gear