Combine duplicate, sequential values, then group into a range

Hi,

Here's what I'm trying to do:
1. Check column B to determine if value "2" is a sequential duplicate
2. If so, combine the sequential duplicates of "2" THEN
3. Insert a new column, AND
4. Assign a letter to the new column, which defines the range of how many sequential duplicates were combined

Please see attached spreadsheet for a visual explanation.

I'm trying to create a macro for this process since I have tens of thousands of rows to format this way.

Any help is very much appreciated!

Thank you.