The solution that currently exists will provide full functionality of the 8.4 MTC bezel, with the exception of the highest speed on the blower, speeds 1-6 work fine speed 7 does not, all else works both ways soft and hard buttons.
That said currently this solution works only on trucks that do not have the extra 5 pin fan control plug. The easiest way to know which one you have if you already installed the 8.4 is if the onscreen fan graphic only goes to "4" or by counting the number of clicks in your current fan dial.
If your onscreen fan graphic goes to 7 you do not have the extra 5 pin plug and this harness will work for you for everything except the 7th speed on the fan, personally I could easily live with that but alas I do have the 5 pin plug.
I tracked down where to buy all the plugs and the required module, I also have the pin-out to fab the harness. I along with others are trying to figure out how to make this work with the extra 5 pin plug.
The cost for this if you DIY would be about 100.00 give or take, plus whatever you pay for the 8.4 bezel.
Surprisingly the answer was staring us all in the face, but also required a few leaps of faith and of course tracking down the parts and the connectors the 5 pin was the trickiest.
The primary credit for this really goes to the getupkid, who like myself has the extra 5 pin plug and can't yet himself use it.