stored procedure slower when called through c client than pgadmin

We have a stored procedure that takes two integers as parameters, a start date and a stop date.

It runs some calculations on a table and updates some columns in the same table.

The table being updated is partitioned.

The server version is 9.1.8.

When we run this stored procedure through pgadmin it runs in around 10 – 15 minutes.

When we run the same stored procedure through our c++ program that is using libpq it takes 1 hour.

Anyone have some insight on what could be the difference?

Thanks,
Brad