I have to second Zentara's comments about using ptkdb but I can offer one caveat. While it does a wonderful job moving through subroutines, make sure you don't try to move through a module's subroutine - unless it's one of your own - because you're going to see a lot of stuff that won't make sense. Just use step over instead of step in and you'll be fine.

Besides that small niggle, I'd be lost without it in my toolkit.