Green’s Dictionary of Slang

(US) exhausted.

1914		Pullman Herald (WA) 13 Mar. 5/2: The Davenport boys were pretty well pepped out as they were small [...] and could not stand the hard grind.
1920		F.S. Fitzgerald This Side of Paradise in Bodley Head Scott Fitzgerald III (1960) 122: Don’t say a word; I’m tired and pepped out.