Just going to chime in here.. I just completed this upgrade on my IOB truck. I know there was a few of us in here with IOB trucks with questions. Hopefully this helps..
I went IOB to IO6.
My truck is a 2018 Silverado Custom (No steering wheel controls, basic cluster with 7" Screen & Carplay)
Mods Needed:
Denali Or Intellink Cluster (must get it programmed by WAMS if using a used cluster)
Steering wheel w/ steering wheel controls & clock spring
8" Screen (I dont know if theres different ones, mine came off a high country with Carplay and Navigation)
HMI & Radio Module (Provided by MVI Inc)
MVI Harness for IOB to IO6
MVI Harness for Radio steering controls
Run LINBUS wire as previously stated here
The MVI harness is plug & play except for the wires that go into the gauge cluster plug (must be added, takes less than 5 mins to do it)
and the 4 BCM wires.
To get the rear view camera to work (From your big IOB radio plug, unpin the two (Gray/Yellow) Wires and the (White/Blue) wires. There are two of each. Connect Gray/Yellow to Gray/Yellow and White/Blue to White/Blue. (DONE!)
Hope this helps, all in all it took about 2 hours to install.