AC1900 Nighthawk - Can't Find Firmware update under Admin?

I'm not the original poster, but I have just recently purchased the same model (AC1900 Nighthawk) and am suffering from intermittent/slow internet as well. To your questions vkdelta:

I am guessing your ISP is comcast. -> Yes

can you please provide bit more details on your WIFI issues? -> WIFI doesn't seem to be issue, but rather internet

what problem are you seeing? -> very slow connections, often times dropped altogether, rebooting modem seems to remedy briefly, but then problems reoccur

how often are seeing? -> reoccurring. For what its worth, the downstream light continuously blinks green (can't seem to find cause on web)

what device were using before? -> ARRIS Surfboard + Linksys Router (told by Comcast that both were "end of life")

what clients do you have problem? -> all? both laptops and smartphones

what is the version of wifi driver on those clients? -> wifi doesn't seem to be issue with me

where is the device placed in the home? -> central location, using NetGear WIFI Analytics app on my Samsung and all rooms in house seem to have strong WIFI signal

Do you have problem with 2G or 5G ? or both? -> neither

what channels are you running 2G and 5G on? have you tried changing to non-interfering channels? -> 2G is on Auto(11), 5G is on 149 + 153 (P) + 157 + 161 (I'm not sure how to check for interference I'm afraid)

Thank you in advance for any additional thoughts you might have!