My grandma has a 1997 ford expedition and the transmission is slipping?

The transmission started slipping bad so he put 4 quarts of transmission fluid in it and it's still slipping I has wonder if there's any thing else that could be wrong with it or if the transmission is just bad

No way to know what is causing the trouble w/o having a few transmission shops diagnose the issue; go to a few different shops for their estimate of repairs and what warranties they have

Find local shop at ATRA.COM for them to look at it and give grandma an estimate to repair it. Might just be low on fluid and repair whatever is leaking