Yup, I see that driver associated with the SATA2USB3 adapter however the actual data rate is no different that for a non-UAS device (like a WD Passport). Prior to the 10.11.3 update the data rate was much higher. I tried diff'ing the associated extensions from before 10.11.3 and the ones after the update. The files changed according the date but the main difference appears to be in the signing, not the content.
I'll have to keep looking but at the moment I can't imagine what is causing the problem.
Partial ioreg output:
| | | | +-o PRT8@14800000 <class AppleUSB30XHCIPort, id 0x1000002b3, registered, matched, active, busy 0 (401 ms), retain 20>
| | | | +-o ASMT1051@14800000 <class IOUSBHostDevice, id 0x100000353, registered, matched, active, busy 0 (401 ms), retain
118>
| | | | +-o AppleUSBHostLegacyClient <class AppleUSBHostLegacyClient, id 0x100000356, !registered, !matched, active, busy
0, retain 8>
| | | | +-o AppleUSBHostCompositeDevice <class AppleUSBHostCompositeDevice, id 0x100000359, !registered, !matched, active
, busy 0, retain 4>
| | | | +-o IOUSBHostInterface@0 <class IOUSBHostInterface, id 0x10000035a, registered, matched, active, busy 0 (399 ms),
retain 13>
| | | | +-o IOUSBMassStorageInterfaceNub <class IOUSBMassStorageInterfaceNub, id 0x10000035c, registered, matched, acti
ve, busy 0 (399 ms), retain 10>
| | | | +-o IOUSBMassStorageDriverNub <class IOUSBMassStorageDriverNub, id 0x10000035e, registered, matched, active,
busy 0 (396 ms), retain 11>
| | | | +-o IOUSBMassStorageUASDriver <class IOUSBMassStorageUASDriver, id 0x100000360, registered, matched, active, busy 0 (290 ms), retain 9>
| | | | +-o IOSCSITargetDevice <class IOSCSITargetDevice, id 0x100000362, registered, matched, active, busy 0 (290 ms), retain 9>
| | | | +-o IOSCSIHierarchicalLogicalUnit@0000000000000000 <class IOSCSIHierarchicalLogicalUnit, id 0x100000364, registered, matched, active, busy 0 (290 ms), retain 10>
| | | | +-o IOSCSIPeripheralDeviceType00 <class IOSCSIPeripheralDeviceType00, id 0x100000373, !registered, !matched, active, busy 0 (287 ms), retain 8>
| | | | +-o IOBlockStorageServices <class IOBlockStorageServices, id 0x100000377, registered, matched, active, busy 0 (287 ms), retain 6>
| | | | +-o IOBlockStorageDriver <class IOBlockStorageDriver, id 0x100000378, registered, matched, active, busy 0 (287 ms), retain 8>
| | | | +-o ASMT 2115 Media <class IOMedia, id 0x1000003df, registered, matched, active, busy 0 (287 ms), retain 11>
| | | | +-o IOMediaBSDClient <class IOMediaBSDClient, id 0x1000003e0, registered, matched, active, busy 0 (0 ms), retain 6>
| | | | +-o IOGUIDPartitionScheme <class IOGUIDPartitionScheme, id 0x1000003e7, !registered, !matched, active, busy 0 (0 ms), retain 8>
| | | | +-o EFI System Partition@1 <class IOMedia, id 0x1000003ea, registered, matched, active, busy 0 (0 ms), retain 9>
| | | | | +-o IOMediaBSDClient <class IOMediaBSDClient, id 0x1000003ed, registered, matched, active, busy 0 (0 ms), retain 6>
| | | | +-o Macintosh HD@2 <class IOMedia, id 0x1000003eb, registered, matched, active, busy 0 (0 m:
