Green’s Dictionary of Slang

1. (US) top-rank, first-class, socially and otherwise superior.

1882		Nat. Police Gaz. (NY) 2 Dec. 3/3: [H]e asserts of the profession ‘there is always room at the top.’ [...] from his standpoint, ther Is plenty of room, since he isn’t ‘a way up actor’ by any means .
1900		T. Dreiser Sister Carrie 105: The finest resort in town. It’s a way-up, swell place.
1909		‘O. Henry’ Roads of Destiny 299: I want to be manager of something way up — like a railroad or a diamond trust.

2. (US drugs) in a very positive mood, poss. drink or drug-induced [play on high adj.¹ ].

1949		‘Hal Ellson’ Duke 130: I’m feeling cool as hell, like no tiger tank can stop me even. I’m way up.
1955		W. White ‘Wayne University Sl.’ AS XXX:4 303: way up, adj. Drunk.