Per the website:
https://www.gmfleetorderguide.com/NASApp/domestic/vehiclesel.jsp?year=2021®ionID=1&divisionID=2
Technology Package, includes (UVS) HD Surround Vision, (DRZ) Rear Camera Mirror, (UVN) Bed View Camera and (UV6) Multicolor 15" Diagonal Head-Up Display
SLT : 1 - Requires (DQS) outside power adjustable vertical trailering mirrors, (PDJ) Driver Alert Package II and (PDY) SLT Preferred Package. Includes (UHS) 8" Digital Driver information Center.
AT4 : 2 - Requires (PDJ) Driver Alert Package II and (PDO) AT4 Preferred Package. Includes (UHS) 8" Digital Driver information Center.
DENALI : 3 - Included with (PEC) Denali Ultimate Package. Requires (PDJ) Driver Alert Package
It looks like you can get the "Technology Package" on an SLT model, BUT .... you must purchase the large towing mirrors [ DQS) outside power adjustable vertical trailering mirrors ]. However, on the AT4 and DENALI you can get the Technology Package with the standard mirrors.
Makes you wonder if you could order an SLT with the Technology Package (and Larger Mirrors) and then replace the mirrors with the two of the smaller Denali mirrors?