Lyric discussion by PTCGAZ 

Cover art for Truckin' lyrics by Grateful Dead

Personally I think they are lamenting going from smoking pot to doing heavier drugs..

What in the world ever became of sweet Jane? She lost her sparkle, you know she isn't the same Living on reds, vitamin C and cocaine all a friend can say is "ain't it a shame"

But it also has to do with their arrests for possession, etc.