1994 Buick Roadmaster Grinding Sound When Braking

First, I just put in some Mercon Transmission fluid into my car because I could tell I needed some cause I could hear my gears grinding a little when i drove my car. And it would also take a lot of RPM to get my car to move in reverse.

Then I soon realized I needed to use Dexron fluid.

Second, a day later now, I get a grinding noise everytime I come to a stop. This didn't happen until maybe a day after I filled my transmission fluid up.