When I was in Chicago on vacation, I tethered to 4G and got 9MB/s down. Although the coverage was great there, so maybe that's the issue.
My 4G speed are fine with the phone.
Enabling WiFi 4G Tether starts fine.
The client download speed is just very slow (0.3Kb). Upload is fine (1.3Mbps)
When the same test is done with 3G. Everything works fine.
It has been reported in xda about this issue. It seems Virgin/Clear is blocking tethering under 4G and thus you need to use a proxy.