I've been receiving a lot of feedback about this module so I just updated the repository with the latest code I've been using on a 4.6.6 install. I've never tested it on anything outside ver. 4.6.X
I also crated some crude install instructions for X-Cart, The Tag Manager config is up to you, but all the variables should be in place when you need them.
https://github.com/INTPMarketer/X-Cart-Google-Tag-Manager