How to connect a Nexus 6p to Windows 8.1 in MTP mode

When I connect my phone to my Windows 8.1 PC, I can select PTP mode on the phone and the phone immediately shows up under "This PC". However, I only see pictures related files, I wanted to see other media. So I try to select MTP on my phone, and as soon as I do the phone icon disappears from "This PC" and does not reappear. I don't see any error messages, prompts to install drivers, etc. I read somewhere that in Android, under settings -> storage to press the menu-button and choose usb-connection, but the menu only shows "Help & feedback". I have tried both with USB debugging enabled and disabled. On my Windows PC, under Device Manager -> Android Device I see "Google Nexus ADB Interface"; trying to update it says the latest version is already installed. I tried uninstalling it, and reconnecting the phone, but this just automatically reinstalled the same driver. I also looked under every other entry in device manager and there isn't anything else related to ADB or MTP. I don't see any kind of separate MTP driver though. If I try to update software manually and how compatible hardware, it shows: "Google Nexus ADB Interface" and "USB Composite Device" and nothing MTP related. I found my device under "Devices and Printers -> Unspecified". When I tried to troubleshoot, it says "Google Nexus ADB Interface is an older USB device and might not work with USB 3.0. Plug the device into an available USB 2.0 port..." But I've only got USB 3.0 ports! If I go ahead and have it finish the troubleshooting it says: Problems found: Google Nexus ADB Interface can't work properly with USB 3.0 (Not fixed) What?! The fact that PTP *does* work seems to contradict this, right? And since when has USB 3.0 not been backwardly compatible with USB 2.0 devices??? How do I get my PC to recognize the phone in MTP mode?