Sir Sudster beat me to the response, but I would have said what he said. The first place to go to improve efficiency is your process parameters. Mash conditions such as pH, temperatures, mash volumes, etc have a great effect on efficiencies as well as lautering equipment and conditions. Another factor could be the malt you are use to using versus the Briess Pilsen malt. If you have been using an imported malt from Europe and have started brewing with domestic 2 row malts, you will see a change in the final gravities and efficiency. The reason for this is the malt extract of European malts is a bit higher than domestic malts as it has to do with barley varieties and growing conditions. US/Canadian 2 row varieites of malts give fine grind (dry basis) extracts (read ideal extracts) of 80 - 80.5%. European malts give extracts in the 80.5 - 83%. This will give you more extract (final gravity) per pound or ounce of malt used. If you use the a domestic base malt in a recipe and then switch to a European malt with the same quantities, you may see an increase of final gravity of 2 - 3 Plato (10 gravity units).
I hope this helps.