I Have a Tingly, Cold, Slightly Cavity Type Sensation Under my Crown?

You have stated that the tooth had a post and crown already.  If that is the case there is no way the tooth can be sensitive to cold.  I would check to make sure that it is not an adjacent tooth that is the problem. 

You mention that the tooth has endo and a post. A tooth without a nerve should not have any sensation to cold. There might be an additional nerve canal in the tooth that was not treated, or the sensation might be coming from the adjacent tooth. It is usually very difficult to remove a permanent post from a tooth without risking fracture of the tooth. I would seek another opinion from the endodontist BEFORE removing the post.