Dry Scalp, Flaking, dandruff shampoo does not help

Hi,

For several years I have had a dry, flaking scalp.  Using dandruff shampoo doesn't help.  I've tried T-Gel, and while it seems to alleviate flaking for 12 hours or so, it has no long term benefits, even with regular use.  I've tried shampooing my hair less often to allow natural oils to build up, but this doesn't seem to help.  I've tried using moisturizing shampoos and conditioning regularly, but this also doesn't seem to help.

Any tips or advice will be greatly appreciated.