Rsham Mana Issues

I am a new RSham who is struggling keeping up mana. I am 51 points specc’d into Resto, I have good/pre-raid BIS items except for belt and pants, and I down rank healing wave to rank 5, chain healing to 1 when I can. Despite this, I am always running oom in dungeons. I wonder is this just RSham life or am I missing something?