I believe it originates from trucker jargon, where a trucker puts the pedal to the metal, so that he can get his truck going fast, since truckers often get paid by the shipment, and the faster it is delivered, the sooner they can start another run. Ref, the song "Convoy," from the 70's, about the same time as the CB radio craze that swept the nation in about 1974. See also, Smokey, flip-side, and "got your ears on."
10-4 goodbuddy.