Dishwasher leaving a film on dishes in the rinse cycle and I'm using the same detergent since it was bought new.

Unfortunately, even though you are using the same detergent brand (and version). The detergent formulation has changed. The phosphate compounds in the detergent have been removed. The phosphates improved the cleaning action in the old formulas significantly by keeping the calcium and other mineral ions from redepositing on the dishes. They also helped improve other parts of the cleaning process.

If you aren't using a rinse aid, try adding some to your dishwasher. Otherwise try other brands and formulations of detergent to find one that actually works. Recent tests by Consumer Reports gave the best grades to the the Finish Quantum and Powerball tablet detergents. (However, both of these ranked lower than the 2010 test best product due to the phosphate-free formulas.) All of the powdered phosphate-free formulas ranked at the bottom of the list.

I wish that I had better news for you.

Cindy Wells
(We went through a similar issue with our dishwasher detergent. The Consumer Reports test results are probably available at your local library if they subscribe to the publication. Otherwise you can pay a fee to access the content online. I read a review of the chemistry issue for the detergents in the Jan 24, 2011 issue of C&EN, which may be in a Chemistry or University library near you.)