Is it ok to go direct to my ex-employer to ask why my pay was lower before I file with EEOC?

I was assisting a laid off person by my ex-employer to find a job when he told me how much he had made while we both worked at the ex-employers company. I was angry upon learning that my equal coworker, whom I had seniority, and whom I trained on some aspects of the job had made a very substantially higher amount as compared to my direct payroll compensation from the company.
I feel 100% certain that I have been discriminated against based on belief that my friend would not lie about something like that, but I also feel compelled to tell my now ex-employer (I took another job)what I have found out and how I interpret it, and that I intend to file an eeoc pay discrimination claim, but wanted to give them the opportunity to address it before it went any further. Is this an ok (legally ok?)thing to do? Can they retaliate with some kind of lawsuit against me if I do this and say we still do not agree about the reason for this difference and I file the eeoc claim anyway?