Were you given any total scores on achievement? I am just wondering if anything would be at DYS level, because the verbal score certainly is.
You can see the highs and lows on the achievement testing, where certainly anything that is timed, he does not do well on, but that is to be expected. Does he seem frustrated? It isn't unusual for gifted kids to have a lower processing speed and/or working memory. Your son's WM is quite strong, so that is good.
Do you see perfectionist qualities? Sometimes the lower processing speed can also be due to that. So, I guess what I am saying in a round about way that that lower PSI could be due to a combination of factors....his sensory issues, as well as gifted perfectionist qualities.
It is good that he is on an IEP. Make sure that his strengths are being addressed, though and not just by giving him additional work and/or boring worksheet packets
