Green’s Dictionary of Slang

(US) to excess, very much so, intensely.

1854		M.J. Holmes Tempest and Sunshine 8: In the cabins we seen a bright light, and heard the niggers larfin like five hundred.
1914		A.P. Man Jr ‘Further Word-Lists – Virginia’ in DN IV:ii 159: like five hundred, adv. Very fast. ‘We certainly was goin’ like 500!’.