My question involves defamation in the state of: New York

I am almost certain there was some slandering and defamatory comments/communication made about me while I worked at a large investment bank back in 2004. Previous to that I worked at another investment bank i 2002 and got in trouble for behavioral issues with this employer. Many employees there knew about it there. Once I moved to the new investment bank in 2004, it was apparent that they knew about my previous problems from 2002. It seemed much more aggrandized however at the new investment bank in 2004, and people took it much more seriously than they did at my previous employer. I had asked people what was being said about me and if they heard anything about me. I was not working with anyone directly that I knew from my previous employer. I am certain that there were comments made which made me suffer much personal and professional harm to my reputation. I can understand people being weary of me but I am also afraid the truth was distorted and made much worse than it actually was. Is there any way to ascertain what exactly it was that was said about me in 2004? Would hiring a private investigator be worthwhile? What can I do? What should I do? The situation is still painful to me and I want to know very much what was being said about me. Is there anything I can do about this?