I'm wondering if any of you have had any luck deploying tealium via GTM. i.e. Adding the utag.js tag as custom HTML in GTM, and then configuring the relevant extensions etc., I've followed this guide to the letter and trialed and tested various Load Order settings but try as I might it seems no utag or dataLayer variables will pass into Visit or Visitor attributes. I'm hoping to build on top of an existing GTM install without having to re-cut everything and some data in the GTM dataLayer would be tricky to push directly into Tealium.
The article you were working off of was an older way that we used to implement Tealium Collect into Google Tag Manager. We now have a custom template integration available that is easily added to Google Tag Manager and allows collect to fire. It's also compatible with first-party domains, as the URL can be updated to reflect a custom domain.
I hope this helps with your integration!