Truckin ,is considered "pre-Disco" , mainly because it was out before the "Disco" commercial designation came into existence.
Tracks like Truckin ,were played in urban clubs ,households and house parties/social events from the time when they came out. Disco ,being a multi cultural "genre" ,combined dancable Pop and thru the older DJ's ,dancable R&B. Later ,when the mixing of tracks allowed there to be extended versions ,the fact that it was a dancefloor hit ,made it a prime track for a remix or extended mix. It is in fact though ,Funk.