Green’s Dictionary of Slang

a general intensifier, overwhelming, extraordinary, the best, the most fashionable, attractive etc.

1937–84		Partridge DSUE (1984) 1083/1: from ca. 1890; ob.
1961		J. Scarne Complete Guide to Gambling 690: It’s slamming – fast, having plenty of action.
1991		De La Soul ‘Millie Pulled a Pistol on Santa’ 🎵 Around this time the slamming joint was ‘Milik is Chillin’.
1983		R. Klein Jailhouse Jargon and Street Sl. [unpub. ms.].
1998		Source Oct. 22: It’s not slammin’ and barely worth checking out.
1999		Guardian 12 Oct. 43/2: Synonyms for exciting [...] ‘kicking,’ ‘slamming,’ ‘blamming’ and ‘storming’.
2000		N. N. Barlay Crumple Zone 64: It’ll be a slammin’ night.
2004		Eble Campus Sl. Apr.