The trucks gain/gather 'speed' as they drive down the hill. = The trucks pick up 'speed' as they drive down the hill. [=the trucks go faster as they drive down the hill]
He types at a 'speed' of about 50 words per minute. = His typing 'speed' is about 50 words per minute.
Let me 'bring you up to speed' on our plans. [=let me tell you about the changes in our plans]
(..) any hard words of late? No, my good lord. But as you did command, I did repel his letters and denied his access to me That hath made him mad I am sorry that with better speed and judgment I had not noted him I feared he did but trifle and meant to wreck thee Come, go we to the king. (..)2015 Hamlet
(..) Married with my uncle, my fathers brother But no more like my father than Ito Hercules... within a month! Oh most wicked speed, to post with such dexterity to incestuous sheets It is not, nor cannot come to good. But break, my heart, for I must hold my tongue - Soft you, a word, my lord - Horatio? (..)2015 Hamlet