One of the best tests to perform is the modems LAN Speed Test, this helps pinpoint if the issue is local (Modem, cables, router, computer NIC). The HT1000 should almost always get between 20 and 35Mbps on such a test when going through a router, where as the HT1100 if the network is full Gigabit should get between 150Mbps and 210Mbps.
The next issue is, a router is more than a divider, it has to handle all the connections. Just because there is a single PC on that router, doesn't mean that there is a single connection. If the router chokes up when there are 500 links being created and they all have some traffic, then speed/response issues WILL occur. Just a tip, you might visit a website, but as many as 1000 different connections are being created or more, Skype alone, when it initially logs in attempts to connect to well over 300 different addresses for advertisements, updates, log-on authentication and more. That's just skype, on one PC. If the routers processor and RAM can't handle that much, then you will get slow speeds. This is why it's important to have a proper router with plenty of internal RAM and processing capabilities.
Tests I perform when it comes to slow speeds/responses.
1: Modems LAN Speed Test - Is it testing GOOD? If so, go to next step.
2: WinMTR to
www.google.com for 10 minutes. This lets you see average latency as well as spikes at every single hop, it sends a continuous ping to each hop inspecting it. Do all results fall under 1000MS for Jupiter platforms? If yes continue.
3: Load up testmy.net, test, do speeds fall between 50 and 90% of plan speeds? If yes, continue.
4: Loadup speedtest.net and test using various servers located NEAR the gateway (Alan, you should have an idea of figuring out where gateways are, like BIL is Billings Montana)
5: Test using P2P, as this mimics generating hundreds of connections, but also has a drawback, it consumes vast amounts of data. Find a GOOD legal torrent that has hundreds, to thousands of seeds that will provide you 20Mbps or more at any time while on a cable connection.
When doing test #5, please note the modem may glitch and cause a short outage for the download, but it isn't very common. If the speeds never reach 50% at a minimum for a sustained period of time, and the modem isn't tripping statecode checks, or the GUI for the modem hasn't become sluggish, it's ALMOST safe to assume it is the router having difficulties processing multiple connections.
6: So far everything looks good, next question is to see if the client is using a laptop, are they using the Wifi, or are they plugging in? If they are plugging in, MAKE SURE they are NOT connected wirelessly at the same time, this can cause serious traffic confusion and collisions with the router. If they are wireless only, pull out your smartphone, and load up an app which detects 5Ghz and 2.4Ghz wireless signals. Some apps can pick up signals even if the SSID is hidden, but can't show the SSID, but lets you know the signal is there. Check the channel that signal is on, and make sure it's not the same channels as the customs.
7: Make a backup of the router configuration, then do a firmware recovery/reset, restoring the router back to defaults, then re-run setup just enough to get it back online and test, did things improve? Find the differences between the two setups, and apply the differences one at a time.
8: Does conditions improve if the router is reset? If so, you may need a new router in the near future, as it's not killing states properly, or it's just worn out from use.