OpenWRT and usb tethering with MiFi 8000

I have MiFi setup as usb tether to a GL-AR750. The connection is detected, and I can get an ip address, but I only get 10mbps download speed. When I connect to the MiFi hotspot via wwan I can get 40 mbps but ping time is increates.

My direct connection to the MiFi via wifi from my phone is 70 mbps, so I am looking to get that full speed. I don't really care that much if it is from wwan, but would prefer usb as it would not cause or receive interference from other devices that way.

Any idea on why my speeds are so slow on usb vs wwan (extender mode).