Hehe well the haste thing could be definitely it. I am running with like 5% haste in my disc spec, but I reforge to haste when I go shadow. If I forget to reforge back when I go disc then I really feel it. Normally I can cast my rotation almost nonstop, but that is with a good 1500 or so more spirit instead of haste. At these lvls of 7-8k spirit, I do have to hold back, quite a bit often. So if you used to have a lot more spirit and lost some with the upgrades, that could be it. I make sure all my pieces have spirit in them by default, and ideally no haste at all, and I then reforge haste and mastery to crit. I didn't feel comfortable until I started hitting that 10k spirit limit. I see a lot of spots you have gemmed intellect, if you focus your gemming to spirit that would probably get you to good levels. Of course if you share gear with your shadow spec it gets tricky. The way I resolve this usually is: If my dps was what was holding the group back when I went dps, I would gear for that, otherwise I would gear for healing.
A difference of 1-2k spirit can really be felt in the long run. Doing some very rough math in my head, changing just 1k spirit into haste and continuing with the same rotation would amount to running oom about 10-13% earlier. 2k spirit would be a considerable effect.