Verizon's newer USB730L modem works well with the ASUS RT-AC5300 as long as you're not using 192.168.1.0/24 as your private IP space. Settings within USB730L accepted changing the default IP space on the modem but after a restart kept defaulting back. Resolved by changing my RT-AC5300 routers LAN space.
RT-AC5300 Router Steps:
1.) Change private IP space of RT-AC5300 to non-overlapping space (e.g. Verizon default is 192.168.1.0/24 and defaults back after a restart (Default: Previous DHCP leases will expire in 24hrs)
2.) Ensure RT-AC5300 router has correct default gateway to new space, mine did not automatically update and was still 192.168.1.1 even though my IP space was 192.168.2.0/24
3.) Select USB Application > 3G/4G
4.) Enable USB Mode and Select USB Device (USB Modem) and leave all settings at default
5.) Within WAN Menu/Level (same as above) Select Dual WAN and change Primary WAN to USB
6.) Apply and wait for restart then proceed
Verizon USB730L Steps:
1.) Login to USB730L via Windows and set connection preference to 'Auto-connect if not roaming'
2.) Tether to USB730L modem via USB 3.0 or 2.0 port to allow the router auto negotiate settings (including routing table)