With my previous host I had a static IP now that I have changed my
host I have a shared IP.  I have a very good ranking with Google but I
have been told that having a shared IP might affect the ranking
drastically in a negative way, is that true?

Hi, 

No, there's no difference in the IP ranking you are talking about.
Shared IP's or virtual domains sharing IP's are pretty common. ISP's
and guys like me, use them too keep the costs of having several
domains on one server, down.

You may see a drop in your Ranking because of the move, that is a
strong possibility, as your domain is no longer at the same IP as
before, but that should come back up, keeping in mind that nothing
else changes, in about two months. As long as your Domain name is the
same, you don't have much to worry about.

Thanks, 

webadept-ga