The current Mac Pro was announced in 2013 and released at the end of that year. It has never had an upgrade and has basically been written off as a failure. The problems are too many to mention in this article.
There are rumours though of a new Mac Pro though and it is sorely needed. In this video from Zone of Tech, Daniel describes the potential new Mac Pro. There are probably some people, as powerful as the iMac Pro is, who might be better served with this new Mac Pro.
This video is well worth a look: