Something like this:

SET ANSI_NULLS ON;
SET QUOTED_IDENTIFIER ON;
GO
CREATE PROCEDURE [dbo].[AppTracker_Milestone_Dates_Browse_SP]
    @UserName VARCHAR(51),
    @DecisionDate DATE,
    @State...

Maybe two separate hashes: (1) all the other columns and (2) the 4K column alone?

Trim it within the SELECT statement:

--insert records into $Sheet1 of Template
SET @SqlCmd =    
'INSERT OPENDATASOURCE   
( ''Microsoft.ACE.OLEDB.12.0'',''Data Source=' + @ServerShare + '\' + @ExportFileName...

There should be some way to copy the file even with the "busy" flag on.  Then open the copy, not the original.

That is, the logic becomes:
check for...

For 3 varchar values, it's tricky, and I'd have to do some testing/experimenting first. 

For 3 numeric values, it's easy to list all 3.

For only 2 values of...

It looked you also wanted to list the specific values found.

That's easy for two values, much trickier for 3 (3 numeric values is easy, but not 3 char...

SELECT pid
FROM @table1
GROUP BY pid
HAVING COUNT(DISTINCT gcode) = 3

I don't understand why you don't have p1 and p3 in your result set.