I have a 2019 SLT without the NHT/Max Tow, but with the Z82 trailering package, factory trailer brake controller, trailering app, and the IOT radio. The truck did not come with the trailer TPMS; not only did it not come with the sensor, but it also didn't come with the module that goes behind the rear license plate. Not realizing that a separate module was needed, I ordered the sensors first. That obviously did nothing, as the truck did not recognize them. So I then ordered the module from eBay. My truck had the wiring harness already ran to module location, so when the module arrived I just plugged it in. The trailering app immediately recognized the module and gave me an option to set up the trailer TPMS sensors. No dealer programming necessary. It was all plug and play. I had America's Tire install the sensors, and I then used my TPMS tool (Amazon, same one for doing tire rotations) to program them. It works perfectly. The trailering app now displays the tire pressure and temperature for all 4 trailer tires.
Just thought I'd put this out there in case anyone is wondering if this can be added. I read a GM tech article where the writer indicated that it could NOT be added after-the-fact, but that is clearly not the case.
Here were the items I purchased to make it all work:
Sensors, part #84152501. $65 new on eBay for a set of 4.
Module, part #84458180. $77 new from GMPartsDirect.com
All-in for about $150.