One solution would be to create a global page load rule that loads your external script at, for example, "Page Bottom". In the "JavaScript/Third Party Tags" section, add a new "Non-Sequential" script. Then use something like the following to append the library to the page:var script = document.createElement('script'); script.src = 'http://example.com/js.js'; // your script URL script.onload = function () { //this is only necessary if you need to call something directly after the script loads }; ...

DTM doesn't really have "tags" in the sense that Tealium does for third-party tools. You'd need to create a rule and then get your code to work in the JavaScript/Third-Party Tags section within the specific rule. There really isn't any documentation beyond that, although I'd recommend looking at the DTM Load Order graphic that is available in the documentation to help determine the proper timing for your code.

We are not. It turns out the site developers removed the call to _satellite.pageBottom() on some pages and that was the cause of the issue.