Exact same problem here with the Wii shop on my Wii U. I called Nintentdo and the tech support rep said it was an issue with my Verizon FIOS router. I have no issues downloading from the Wii U eShop. I tired the following:
- Wired USB and Wireless
- Changed DMZ
- Lowered FW settings
- Put Wii U in the DMZ
I'm glad to see I'm not the only one, but I would like to see this get resolved!