Green’s Dictionary of Slang

distance n.

In phrases

go the distance (v.) [boxing/horseracing imagery]

to commit oneself wholeheartedly.

1937		J. Curtis There Ain’t No Justice 32: I said a dollar if you got put out, a oncer if you went the distance and lost, and thirty bob if you won.
2000		N. Barlay Crumple Zone 226: And like he keeps saying, he’ll go the distance. Especially if he thinks either of us hasn’t been straight with him.