If you looked at PF1 with archetypes and hybrid classes you have a host of investigator builds for bard, rogue, and an investigator class, with flavors like vampire hunter among them. For spellcasters you've got Inquisitors which are like martially trained priestly lawmen, oracles which have archetypes for medium, theres's alchemist, the new fangled arcane classes with a Victorian/Gothic flavor Occult classes: kineticist, mesmerist, occultist, psychic, and spiritualist. Vampire Slayer is a base class as well. A witch though a bit older in flavor than true gothic can still be a fit. There's also third party off-shoots of alchemist with Mad Scientist. There are many classes and class archetypes that fit Gothic Horror. I don't think you wanted not-quite-DnD, but PF1 is pretty close to 3.5...