Slow speeds with Verizon 4G LTE USB modem compared to with Cradlepoint router

Anyone else using a Verizon 4G LTE USB modem in the RT-AC66U? What are your speeds like? I've done quite a bit of testing with my Pantech UML290 plugged into the ASUS vs a couple other routers I have that are specifically for mobile broadband connections like my Cradlepoint MBR1400 and I'm consistently getting higher download and upload speeds with them than with the RT-AC66U.

I've run numerous speed tests on different servers at Speedtest.net and tested multiple firmware versions including the latest beta 3.0.0.4.372.0 and with the ASUS my download tops out at 18-20 Mbps with periods of only 10-14 Mbps and my upload speeds never get above 3-4 Mbps, sometimes as low as only 1.5 Mbps. On the Cradlepoint MBR1400 I consistently get 21-25+ Mbps download and 10-15 Mbps upload. Plugged directly into my Mac using Verizon's VZAccess software I get speeds equal or slightly better than with the Cradlepoint.

I'd like to get rid of my Cradlepoint routers and use just the ASUS but I hate to trade better wireless range and speeds for slower internet. Does the RT-AC66U just need a better modem driver for the Verizon Pantech UML290? I opened a ticket with ASUS last week and have already sent engineering my network test report.

Here are my 3G/4G settings in the RT-AC66U:

Location: USA
ISP: Verizon
APN service: vzwinternet
Dial Number: *99***3#
Pin code: <blank>
Username: <blank>
Password: <blank>
USB Adapter: Auto