If a label has been created for a few days now...there's a 99% chance it's in Louisville, at Tmo's main hub....waiting to ship out, and then tracking will be updated when it gets its origin scan. Totally normal.
Then my question to T-Mobile was as well, "How come my device has sat in your warehouse for two days?" Their answer was they shipped it out and are waiting for UPS to pick it up. UPS' response was they were waiting for T-Mobile to release the device. Either way, my device will now have sat in T-Mobile's Kentucky warehouse for three days. I only started an investigation because that is what T-Mobile said to do. They said if there is no movement on my device for two days, to have UPS investigate it.
I've shipped items for probably 15 years. I've preordered every iPhone that was available for preorder, and even some Android phones. A device has never sat in a warehouse with a created shipping label for multiple days after being charged.