When I had my Mark VIII with over 100k miles and was driving it over 500 miles one way to my job, I was thinking about replacing the fuel pump as preventive maintenance. I asked a NAPA parts guy how long did they typically last and he said some last 30k miles and some last 300k miles and there was no way to predict how long they last. However, if you want to make as sure as possible you don't have a fuel pump failure, replacing it is one way. I traded the Mark at 113k for a new Dodge Magnum Hemi.