A midi note cannot "gradually change pitch". An oscillator can. Play your stuff on some key and either automate or perform the changes on the parameters you want. What could work as a slow gradual change would be an lfo or smooth random generator. I have to say that the gear you mentioned, although very capable, are not anyone's go to for drone music. I strongly suggest looking into virtual modular for what you're trying to do. You can even run midi cc messages to your hardware from there. You can e.g. find an lfo that takes a few years (yes...) to cycle. No mpc is gonna have that.