When I set up Zen cart the first time to try it out and learn how to configure it all I installed in on the same version of Debian, MYSQL and PHP.
I accepted all the defaults i.e. localhost and it worked fine, no problem then.
Now I am trying to install the latest version with Paypal and I am not able to connect to the MYSQL server when I change from localhost to what it should be on a live server.
This is confusing???
Is this on the same server as the first install that worked?
If so, why have you attempted to change from localhost?
Are you using a host for this live install or is this on your own server?
If on a hosted server, contact them for the DB connection details.
If your own, what is your uplink speed/connection? As most uplinks are about 1/10th of the download speed and trying to serve a site will be slow.
This is really not a difference between versions, but more to your LAMP setup. How to access the DB can be configured differently as the SU desires, and these factors need to be passed to Zen Cart to be able to connect successfully.