The T-Mobile version of the LG G3 recently received the update to Android 6.0 Marshmallow. Developer AutoPrime was nice enough to take the image and prepackage root with it! The flashable prerooted D851 30D build is now available for download. The build is also rootable with the KingRoot app.
AutoPrime has a full list of instructions as well as download links at his original thread which you can find at the link below.
via XDA
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