I have super-thick hair, curly too, ever since I was a teenager, and I found that when I stopped using shampoo, my hair and scalp didn't get oily and itchy anymore. No more dandruff. It took about 2 weeks for my scalp to stop producing so much oil. (in the meantime, it felt icky, so I kept it clipped up or in ponytails lol)
The scalp needs massaged well with fingertips to loosen dirt and oils, with plenty of water. I use just conditioner to wash with (something with coco-betaine works really well) a couple times a week, and it helps loosen the dirt and oils, get rid of tangles, and doesn't irritate and dry the scalp. I use a soap bar a couple times a week, and then the remaining days, just rinse really well. During the summer, I wash it every day, but not during the winter.
Like someone else mentioned, a hand-held showerhead with an adjustable sprayer is a MUST for thick hair. So you can turn it on the high-pressure setting to wet hair all the way to the scalp, and also to rinse thoroughly. My hair is so thick that I can't even wet my hair all the way without good water pressure, let alone rinse well.
As far as the soap I use... I alternate between a few, but the one that works the best so far is one I made that's over 50% lard, with some avocado oil and jojoba. My hairdresser used it last time she did my hair also, and she didn't even need to use conditioner afterwards, just combed right through it with hardly any tangles.