Slower 4G LTE speed when connected to Sonicwall TZ300

Greetings,
I am using an UML290 USB Modem connected to a  3 foot USB cable that connects into the Sonicwall TZ300 Router  as our primary WAN connection in a very rural area.
The connection works good enough with bandwidth speeds consistently  at 9.0 Mbps down / 2.0 Mbps up.
The issue is.......
When I disconnect the UML290 from the Sonicwall TZ300 and connect it to my laptop's USB port and place & point the USB modem in the exact same location as it
is placed when connected to the Sonicwall TZ300 the bandwidth connection speeds are much higher at around 23 Mbps down / 10 Mbps up.
I have removed the 3ft USB cable and placed the Verizon modem directly into the USB port of the Sonicwall with out any increase in connection speeds.
I have no bandwidth limiting settings configured in the Sonicwall TZ300.
My questions are:
1) What should I look at / review in the Sonicwall TZ300 to determine if the Sonicwall is limiting bandwidth speeds?
2) Is this a known issue?
3) Is it possible that Verizon is limiting bandwidth when the UML290 is connected to a "Router" ?

Any insight into this issue is appreciated.
Thank you,
Com1