Roku 3600 Connection Fails for Software Update

I just purchased a certified refurbished Black Roku 3600 HDMI stick. My ISP is Comcast and I am using Comcast's Arris TG862G/CT gateway for my Internet and landline VOIP phone. I am having trouble setting up the Roku stick. I am posting in this forum because it appears the problem may be network related.

It connected to an open HDMI port to my TV with no problem and I can see its startup screens. It found the SSID of my TG862G/CT gateway as well as a few other protected WiFi access points of my neighbors. When I entered the default SSID password for my gateway, it took a few seconds to show a green check mark for the WiFi connection, a slightly longer time for the green check mark for the LAN connection, and then it took maybe 15 seconds for a green check mark for the Internet connection. The screen changed and showed a preparing to update software message. About 10 seconds later, I saw an update status screen that never went beyond 0%. After that, I got an update failed message with an error code of 003. My only option seems to be to try again or try a different WiFi connection. All future attempts went directly from the preparing to update screen to the error 003 screen.

Logging into the gateway's web based user interface shows the Roku connected with about a -60 dB signal strength. I tried relocating the Roku stick from plugged into the back of the TV to above the TV with an HDMI extension cord. That didn't help any.

I tried Google searches to see if others had my same problem. I could not find one for my particular hardware combination. Discussions of the 3600 having network connection problems in general seemed to be related to DNS resolution problems, with suggestions of using Google's 8.8.8.8 server instead of the ISP's server(s). The gateway is using DHCP to configure the client network devices. Doing an IPCONFIG /ALL on my connected desktop PC shows it is using automatically set 75.75.75.75 and 75.75.76.76 for DNS. I could not seem to find anyplace in the Gateway's user interface to change the DNS IP addresses it gives out. I have not found any information on viewing or changing any network settings on the Roku stick.

Unless I can get suggestions for other possible solutions, my next step will be to dig up and hookup my old WiFi router to the gateway and see if I can get it to get a working connection for updates and probably viewing videos.

I am tempted to think that Comcast may be blocking the Roku connection with bogus DNS results in an attempt to discourage potential cord cutters.