First, for the search minded for all of you I have read the following threads: https://forums.macrumors.com/threads/2009-mac-pro-fan-control.2057079/ https://forums.macrumors.com/thread...ntrol-1-4-8-1-totally-out-of-control.2055699/ https://forums.macrumors.com/thread...ems-with-non-apple-video-cards.1685629/page-2 https://forums.macrumors.com/threads/7950-mac-edition-fan-speed.1566964/page-2 Here is my situation. I have the following video cards. I have XFX 8GB RX-480, a Diamond Sapphire R9-280X, a GT-120, and AMD 5770 (The last two are Apple Branded). The RX-480 had been running in my PC machine, but I wanted to get the improved performance on my Mac Pro. Previous my MacPro has been running the R9-280X without issue. I got the GT-120 from work for free and I decided that boot screen might not be a bad idea, since I was considering adding BootCamp to this machine. First Setup: RX-480 and GT-120. No issues on Boot, all screens as expected, fan behavior normal. Machine went to sleep, pressed keyboard for wake, PS and PCIE fans go to max. Second Setup: RX-480 and 5770. Same Result. Third Setup: Reverted to R9-280X and GT-120 and got the same result. Can't do the obvious 4th setup because the 5770 and the R9-280X require too many onboard PS connections. So a couple of questions and then a proposed course of action to see if there are any better suggestions. I am running Mac Fan Control because my processors are upgrade to 5680s. I don't mind running the software, I just want to make sure this isn't happening because I am actually melting something that I can't measure. Also of note, while the fans are at max and before they go to max speed, there is nothing really out of the ordinary with temperatures. I don't understand why having two video cards suddenly freaks out the SMC, other than the empirical evidence of that it happens. I have reset NVRAM and SMC. So advice I am looking for? 1. Is there a best configuration of two of these cards in particular slots that makes the most sense? The ideal setup would be the RX-480 the GT-120 since it preserves the most PCIe slots while still giving me boot screens, etc. Theoretically, it would also produce less waste heat than other options. 2. Are there particular slots that might offer better results than what I am getting now? 3. Is the XFX RX-480 card just going to cause me heartache (I know there have been issues with these cards before) and I should move on to a different combination in the interim (keeping in mind I still have the issues with the other two combinations). 4. If the only way to make this work is Mac Fan Control, what should I take the PS and PCIe measurements from and what are the ideal settings? 5. Are there other PCI issues or hard drive configurations that should be considered that might reduce stress/temperatures that could be affecting this issue? I currently have both optical drive bays filled, and 3 of 4 hard drive bays. I have a PCIe storage card for an SSD, a USB-3/C PCIe card, and the two video card combination currently under discussion. 6. Why doesn't this seem to come up more in discussion with people using one or more video cards, or is this one of those solved issues that everyone (other than me apparently) has seen before? As always, any help comments, etc. would be great!