There are several things to check, but I know with my '92 and '91 Grand
Prix's, the brakes always seemed that way, though it was not dangerously
slowly, the brakes never worked as well as the ones on my other cars, even
after all parts were checked out and/or replaced.
You should check out the pads, fluid level, and bleed the lines if you know
how. Or take it into a shop and get a diagnostic done. Here in Canada,
Canadian Tire does free diagnostics on brake systems, and though they will
likely give you a $800 bill, you can find out from that estimate what is
wrong and fix it yourself.