Incorporate Moving Sum formula into my SUMIFS & also create 3 month moving average

I am utilizing a SUMIFS formula to sum volume from multiple rows based on multiple criteria.
I would like to incorporate another formula into my current SUMIFS formula or create new formula in order to calculate a moving sum, last 3 months instead of total (month indicated in additional column K.)

I would also like to calculate a 3 month moving average based on the criteria from my SUMIFS in column C. (Customer & Region) + Month

Please see attached Spreadsheet, is it a problem that the months are formatted as text?
Revised_Multile vlookup values Then Sum-Example TMS.xlsx

Thank you,
Price

I believe this may be what you are looking for, but please correct me if I'm wrong. In cell D2, paste the following and drag down:

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In cell E2 paste the following and drag down:

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*Forgot to mention that I did format the K column as text for this problem