Hands on with Plasma Active One

It's also used extensively in old western movies released before the 70's (and many after). I'm unsure of the origin but I do know it's used extensively in the western US to mean slow. Gumby is a later version and play on words in that his horse was slow (much like Gumby himself).

According to google it's a slang version of slowpoke which derives from the British Slowcoach.