Update on the ATC mod. I drove the truck this morning and left the mode on floor. Went to a couple places so the truck got shut off for 15-30 mins several times. On the way to the last stop I tried the dash vents from floor. No problem. Floor to split. No problem. Split to Floor/Defrost. No problem. Full defrost. No problem. Then the moment I was dreading, defrost to dash. Took a little longer but it worked! I then went back and forth between dash and defrost several times and it worked flawlessly. Auto mode works perfectly also. So at this point I was pretty happy. Went into my last stop, came out 15 mins later, started the truck. Went to dash, no problem. Dash to defrost, like
@Ghost_RAM said it can take 20 seconds, and 20 seconds later it went to defrost. After that it was much quicker. I went back out to the truck this afternoon and tried it again, dash to defrost and back. Same thing took 20 seconds or so the first time then worked much quicker. So it looks like it just needed some time to fully accept the settings.
Only thing I noticed is when I use the physical temp up/down buttons the temp changes on both sides of the 8.4 (like a dual zone with sync on), can anyone else with this setup tell me if this is correct?