Dell XPS 8500 USB 3.0 (rear) port issues

Purchased March 2013

XPS 8500 Special Edition (white case)

Windows 7 Professional, 64-Bit

 i7-3770 CPU @ 3.40GHz

Intel(R) 7 Series/C216 Chipset

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2 x front USB 3.0 (blue) ports operational at  USB 3 speeds

2 x top USB 2 ports operational at  USB 2 speeds

4 x rear USB 2 ports operational at  USB 2 speeds

1 x  rear USB 3.0 (blue) port unrecognized

1 x  rear USB 3.0 (blue) port operational at  USB 2 speeds

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Had only used the two front USB 3.0 ports until recently and they've both worked flawlessly.  Have now tested the two rear USB 3.0 ports and one is undetected when USB 3.0 thumb drive inserted.  The other port is detected, but only operates at USB 2 speeds (and I get Windows 7 popup notification saying that "This device can perform faster" if connected to a Super-Speed USB 3.0 port).

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The installed Intel USB 3.0 eXtensible Host Controller Driver was version 1.0.5.235 until I installed (downgraded to) Chipset_Driver_RW99K_WN_1.0.4.225_A00 from Drivers & Downloads, which is the only one listed as available for my system (which is odd).  In any case, the rear USB 3.0 port behavior is the same, regardless of which version is installed.

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 I've also updated the system BIOS to version A12, updated NVIDIA drivers, verified that USB selective suspend settings are Disabled, disconnected all other USB devices, etc., but nothing helps.  I've even run the Intel Driver Update Utility, which returns no results.

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Is there anything else I can do to  resurrect these two ports?!  I've ordered a couple of USB 3.0 external hard drives and had planned on connecting them to the rear ports.  I've searched the Dell forums and have noticed other references to this problem, but have found no definitive solution.  I know this is an old system (and topic), but any suggestions would be appreciated. :emotion-5: