Green’s Dictionary of Slang

dicer n.2

[vagrant travellers in the boxcars feel like dice being shaken in a cup]

(US tramp) a fast freight train.

[US] ‘Jargon of the Und.’ in DN V 444: Dicer, A fast freight.
[US]Irwin Amer. Tramp and Und. Sl. 61: DICER.- [...] A fast freight [...] old tramps say [...] from the motion of the train, not unlike that used in shaking the dice.
[US]Ragen & Finston World’s Toughest Prison 796: dicer – [...] A fast freight.