Two years back I spent a month trying to bend an earlier incarnation of GD::Graph to my will. Based on that experience, with the caveat that my knowledge of the package is now stale, I would advise this: Consider the GD::Graph package as a starting point. Make your own copy, and modify it to suit your needs. I don't advise this in general, but this package may be an exception.

I also had the problem of getting tick marks to behave for some quirky data, and would have preferred to just subclass parts of the package to get the behavior that I wanted. Unfortunately, I didn't find the package well structured from a "here are concrete classes that are well-structured for subclassing" point of view. Unless the code has since been restructured, you might run into the same. YMMV.