I'm having a similar issue. I'm running a Lenovo Yoga convertible laptop with Windows 8 Professional. When using the UML295, all of my applications run extremely slow. I can't even launch my Global Sonicwall VPN client software. Many windows I open go into the (Not Responding) mode and freeze up. Interestingly enough, as soon as I unplug the UML295, all frozen applications unfreeze and my Sonicwall VPN software opens right up (assuming I've tried launching it with the UML295 still attached). Through all of this though, I am able to connect to the Verizon network (3G and 4G where available).
However, when I attached the UML295 to another laptop running Windows 7, it doesn't seem to have any issues running the same applications. I do have trouble connectiong to my VPN but at least the program itself will launch and attempt to connect.
If anyone has any suggestions on how to improve performance with Windows 8 and the UML295, please post your comments. I'm running out of options. Thank you!!