Using a Dell Precision M4800 on the domain was fine when not on the Dell PR02X E-port plus docking station. As soon as put on the dock, the laptop became sluggish and laggy.

Turns out it’s a power issue. If the dock and laptop aren’t getting enough power, the laptop will be clocked down to run at a lower speed. Confirmed this by unplugging the power to the dock while the laptop was on it (obviously simulates not being on the dock any more but still).

Anyway. Put a big brick Dell power supply on, and works fine.

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This link helped