Green’s Dictionary of Slang

way up! excl.

(US) definitely! very much so!

[US]Daily Trib. (Bismarck, ND) 5 Sept. 11/5: ‘How have you enjoyed your trip?’ asked the tribune reporter of the president [...] ‘Way up! Never tackled a racket in my life that seemed to cotton up the square thing so much as this little off-hand jamboree. Oh! she’s been a daisy; I tell you.’.