Marie, i'm not sure if you are in SPA for SMAS or Unisphere, but in either you should be able to drill down into the DA's that are showing busy in the diagnostic view and sort the physical disks by activity.  When you find the busy disks you should then be able to double click and drill into to find out the busy volumes, TDAT or Regular device. This should hopefully get you on the right path to finding your culprit.
We have very high DA utilization on a number of directors but not all and so it makes us think it is not likely TDEV's but STD dev's which are carved out of certain Raid Groups. I see nowhere in SPA that allows me to sort/search by Devices if I don't know the specific SG. I do know a DA but no mention of STD device beneath it. How does one approach this?  1 or more STD devs (possibly R6 or R1) of unknown dev ID, believed to be used by 1 or more SG. The only symptom is 90+% utilization on some DA's. Appreciated!
find STD dev with high latency using symstat or SPA