I have a buik regal 1988 with problems?

I got a 1988 buik Regal from down the hill and was driving it back up to my house but on my way up to my house on the freeway it's started to turn off and then and then it would start up again and then I finally made it home and then it died and as soon as I try to turn it on again it would struggle staying on it wouldn't start so I thought it could be the fuel pump but we changed the fuel pump and now it's starting to start again but it's not staying running could use some help figuring out what it can probably be it's been sitting at my friend's house down the hill for a year or two