Ok, one thing you could try is to set the WAN port speed to 1000Gb as I see the cable modem you got supports that. I would do a factory reset of the 4500 router. Power down the cable modem and 4500 router. Disconnect all LAN port devices on the 4500 accept the test PC for this test. Power up the cable modem and allow it to sync with the ISP. Then power up the 4500 and let it come to ready and gain the addressing of from the cable modem. Do a quick speed test on the internet and see what you get. Change the WAN port speed on the 4500 to 1000Gb and check the test again. If you don't see any better results. I would set up the test PC for a static IP on the 4500 and test again. One thing you can try for testing is to turn off SPI firewall settings, test again and see this helps. You shouldn't have to. Just wondering why your not getting full speeds while connected.
I would also check and see if your new cable modem has any user interface like the 4500 does. My cable modem does and you could try access yours by trying 192.168.100.1 and see if there could be any possible user settings that might affect connection speeds to the 4500. Usually there isn't much to cable modems and there pretty much automatic and DHCP everything. Normally cable modems don't have there own internal routers like DSL modems and looking at your modems specs, I don't see any thing tell me there is one. So it should work just as a modem and pass information to the 4500.
I did read in the user manual for the cable modem that it requires the use of a crossover LAN cable instead of a straight thru LAN cable when connecting to a hub or switch. I'm not sure if this has any impact when connected to the 4500 router. Normally the use of straight thru cable is all that's needed. I might contact the maker of this modem and ask for details and see if they have any recommendations. Might also ask and see if there are any compatibility issues, if any, regarding the 4500 router. Some OEMs might do some testing in development to make sure there modems do work with other OEM routers.
If possible, do you have a neighbor or friend that has cable internet that you could take the 4500 and the new cable modem to put on there network and test? I would also have you check a different cable between the modem and router just to be sure. I have seen different cable issues on here and my self. This is just to help weed out possible issues and narrow down where the issue lies.
I doubt upgrading FW would help however we wont rule that out just yet. Let us know how it goes. Hope we can figure it out.
This router does handle fast speeds. Check out post #4 and others that posted there speed tests here:
http://forums.dlink.com/index.php?topic=14261.0 
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Topic: Couple issues (Read 11630 times)