Sorry guys, I'm not meaning any disrespect, but you guys haven't seen in person what I've seen. I'm not buying the neighbor thing or channel thing. It worked flawlessly for two straight days, nothing but 135Mbps, no matter what. Then the only thing I changed was I turned the desktop off in that other room. And now no matter what, it's always 65Mbps. Something is wrong, a setting, the Gateway itself, something. And I'm not smart enough to troubleshoot myself and I'm not buying the channel explanation given the facts above. (worked at 135Mbps NO MATTER WHAT the first two days and now 65Mbps NO MATTER WHAT now. Doesn't matter time of day, desktop in other room on or off, location of laptop, location of Gateway. Nothing matters, always 65Mbps now when the first two days it was always 135Mbps)

Thanks for all of the suggestions, and again, I don't mean any disrespect, God knows I'm thankful for those of you taking a stab at it, so please know I mean no disrespect when I say I'm not buying the explanations here. I would bet money to air that if you had sat in my shoes and seen what I've seen you too would be convinced something is wrong,

Let's let this thread die a peaceful death now, I'll either live with the slower Wi-Fi or call Comcast and cancel and see what FIOS has to offer.

Thanks again for all replies and have a great (BUT SAFE!) Holiday season!

Well, I was all ready to try this, since I've tried EVERYTHING else, including calling Comcast (which was ZERO help because they don't even want to talk about Wi-Fi despite it being their equipment), and no matter what, all I get is the same old 65 Mbps connection no matter time of day, no matter location of laptop (including in the same room right next to the Gateway), no matter if the desktop is on or off, it just doesn't matter. I've reset the Gateway modem so many times I can tell within a few seconds of it being reset without looking at a watch and just going by feel. Nothing matters. First day and a half, blazing 8 to 9 MBps download speeds on Steam and GoG and a 135Mbps connection showing up under properties, and ever since then 3 to 4 MBps download speeds on Steam and GoG and a 65Mbps connection showing up under properties.

The only problem is, I have no clue how to "change channels" or even what the heck that means. I merely posted this in case it's something easy, but I suspect it's modem specific and there's no way of knowing so help here is probably unrealistic but I thought I'd try before I cancel Comcast and give FIOS a call.

Thanks again for all of the responses. It's hard to get people to understand just what we saw when preconceptions about Wi-Fi being "iffy" and inconsistent means minds get made up without hearing us. (I say "us" because it was me and my nephew that witnessed this). We witnessed blazing speeds that first day and half when I had forgotten my desktop was still on, with the Wi-Fi connection showing up all day at 135Mbps. Then, as soon as I realized I had forgotten my desktop was on, I powered it down, and the next time we downloaded something we noticed a drastic difference and that the connection was showing up at only 65Mbps. And now, no matter what, time of day, location, desktop on or off, gateway reset or not, nothing matters it's ALWAYS connected at 65Mbps now.

There are a number of reasons why your download speed might drop (and particularly over Wi-Fi):
-Some ISPs can randomly drop your internet speed. Sometimes it's due to maintenance, sometimes it's because there are a lot of other people using the same exchange/branch at the time of day, sometimes they drop your internet speed and keep it there until you reboot the router so you can either take the lower Internet speed (saving them money) or get inconvenienced with a reboot.
-Any electromagnetic signals in the same frequency spectrum as Wi-Fi can cause crosstalk/interference, resulting in lost data packet transmissions. Wi-Fi has an array of partially overlapping channels assigned to it, at least in the USA - if anyone else sets up a Wi-Fi device in your area, this will likely generate interference even if none of your devices have moved.
-Server-side delays. A link geographically and logically far away from you between your computer and the server might have malfunctioned, forcing a suboptimal reroute. The server might be busy, or any number of intermediate links could be congested.

Can you connect directly (ie without using wifi)? If so, see what download speed you get doing that. That might give you a hint as to whether it's a problem with your wifi or the connection coming to your home, although the direct connection is likely to be rather stronger anyway.

yes, this is modem specific, but you can login to modem settings page and just look through all pages to find word "channel" there. Reading user manual for a modem can help too. It's not a rocket science, you can handle it for sure.

Wireless LAN connections are tricky indeed. For example, I have the phenomena that after some time I lose connection, but as soon as something is physically moving within the radio field the connection comes back. It could be just me turning towards the window or the door. It's just strange and unpredictable.

Anyway, to me it seems that your rooter or modem uses a fall-back standard to support a wide range of even older wireless clients. Older standards, like for example 802.11b transmission standards, do not support higher bandwidth. You want to make sure to use 802.11n for up to 600 Mbit/s. So you will probably have to log into the modem/rooter and change the transmission standard from "mixed-mode" to "802.11n-only" or try to force the use of this mode on the client-side in the Windows Device Manager for your WLAN-network adapter. Make sure all your clients are 802.11n compatible devices or otherwise you will not be able to connect after changing to "802.11n-only" mode.
802.11n standard can use 150 Mbit/s per antenna with a maximum of 600 Mbit/s with 4 antennas. That is for rooter and clients of course. So a rooter/client with only 1 antenna will never reach a bandwidth above 150 Mbit/s.

Others here in the thread are right either. Make sure you have enough channels free. 802.11n mode needs up to 4 channels/frequencies and because you do not want overlapping channels to avoid disturbance, it is commonly suggested to use either one of the following channels 1, 6 or 11. Not sure how good this commonly suggested channels are though, as I have made the best experience using a my WLAN fixed to channel 9.
In general modems and rooters are set to use "auto-channel-search" and switch depending on the quality of the signal, but for a constant data bandwidth it might be better to use a fixed channel.

Other sources for signal disturbance might be DECT telephones, microwaves or mobile phones. You might want to test if one of your devices is causing a disturbance by turning them off and if you could identify it, search for another place where they do not disturb your WLAN.