Passing A SSIS Global Variable To A Declared Variable In A Query In SQL Task

I have a SQL Task that updates running totals on a record inserted using a Data Flow Task. The package runs without error, but the actual row does not calculate the running totals. I suspect that the inserted record is not committed until the package completes and the SQL Task is seeing the previous record as the current. Here is the code in the SQL Task:

DECLARE @DV INT;
SET @DV = (SELECT MAX(DateValue) FROM tblTG);
DECLARE @PV INT;
SET @PV = @DV - 1;

I've not been successful in passing a SSIS global variable to a declared parameter, but is it possible to do this:

DECLARE @DV INT;
SET @DV = ?;
DECLARE @PV INT;
SET @PV = @DV - 1;


I have almost 50 references to these parameters in the query so a substitution would be helpful.

Dan