Is there a keyboard shortcut to navigate full screen windows of the same application? Or is there some app that will let me do it. This bug has been forever since Lion. Isn't it about time apple fixed it?
Witch also includes full screen windows, and ⌥⇥ selects the next window from the current application by default.

Or if you use an application that has its own implementation for full screen windows (like WriteRoom), ⌘` usually includes custom full screen windows.