So, All Saints has historically just sung the Great Doxology in Tone 6 (that’s “Second Plagal Mode” for those of you out there who speak Byz) since time immemorial, and I am starting the long, slow process of incorporating the other seven modes into our liturgical practice. My understanding has always been that it goes with the Resurrectional mode of the week (an understanding reinforced by the OrthodoxWiki entry for the Great Doxology, which is clearly a critical source of no small import), but looking at the AOCNA liturgical guide (online, printed, and L.A. diocese version) it appears that they have it going with the Eothinon (hence being in Tone 5 this week rather than Tone 7). Looking at the Liturgikon, the “Five Pounder” (Divine Prayers and Services, Nassar), and the Antiochian little red service book, a rubric is not provided that resolves the question; in the Kazan Byzantine Project Matins book, the table of contents indicates that the Great Doxology is sung in the “tone of the day” but then the rubric in the music itself has it going with the Eothinon (first Eothinon, Tone 1, second Eothinon, Tone 2, etc.).
Can anybody clear up for me what’s happening here?
Leitourgeia kai Qurbana: Contra den Zeitgeist 
Contemporary Greek practice is to use the mode of the week on Sundays. When the Great Doxology is chanted on a weekday, the general practice is to stay in the same tone as the last hymn that was chanted. For example, on Christmas and Theophany, Second Mode; on Pentecost: Plagal of Second Mode. Contemporary Antiochian practice extends this logic to Sundays as well. I imagine this is for convenience more than anything else. Personally, I chant the Doxology in the mode of the week.
There are some exceptions. On feasts of the Cross, the Doxology is usually chanted in slow Fourth Mode “Agia.” On Palm Sunday, it is usually chanted in slow Fourth Mode “Legetos.” And on Thomas Sunday and January 1, the Doxology is traditionally chanted in First Mode (as well as the Cherubikon and Communion Hymn). These unwritten traditions are not universal, but are widespread enough to mention.
I encourage you to post future questions like this on the Psaltologion discussion forum.
According to the Typikon of the Great Church of Christ by Georgios Violakis (1888): “On every Sunday and every feast of the Master and the Mother of God, as well as on the commemorations of the celebrated Saints, in the Orthros, the doxology is chanted in the mode of the doxastikon.” But in the recently-published Systema Typikou, Fr Constantine Papagiannis notes that using the mode of the week is the more ancient practice. If I remember correctly, the doxology is chanted in the mode of the week at the Ecumenical Patriarchate still.
That’s exactly the kind of informative answer for which I was hoping! Thank you.
We always did the Kazan Byantine Tone 6 at St Michael’s, but here, we always do the “Greek chant” Great Doxology (monophonic with ison, not harmonized). I have no idea what tone it’s supposed to be; it doesn’t say on the music.
Greek Orthodox parishes in the Americas frequently sing the third mode doxology by Sakellarides on Sundays (usually in harmonized form). But this is not representative of either the ancient practice (mode of the week) or the more contemporary practice (mode of the doxastikon).