Slow WiFi speeds

2.4MHz has a max throughput of about 75Mbs. Actually, in the real world, it's more like 45 to 55 Mbs. And that's standing right next to the router. 5.0MHz has a max throughput well over 600Mbs at close range.

So, the very first thing you'd want to do is ensure that you're connecting to the 5.0MHz radio. Some routers have the bands split. Some, like ours at AT&T, have the bands basically "meshed" so that you see the 5.0 when you're close, and the 2.4 when you're farther away.

To the best of my knowledge, Cox doesn't do anything like that. Most of their setups that I've seen had the bands separately named, so you can choose whichever one you want. To be clear, I've never worked for Cox, and I only see their equipment when I'm removing it during an ATT install. So, YMMV.

Once you've established that you're on the correct (5.0MHz) band, you will want to ensure there's nothing out there sucking up bandwidth. No TOR files getting uploaded, no home security system uploading video, no server farm hiding in your back bedroom. Then, assuming that you've connected to the correct band, eliminated the possibility of network congestion, you can take a look at possible 5.0MHz interference.

There are a few cordless phones that I've seen which can cause interference. Nearby aquariums (weird, I know) can cause wifi problems. Fluorescent lights also and mirrors(!). Assuming you've eliminated all of these potential interference sources--and assuming the problem is duplicated across multiple devices--then you can pretty reasonably conclude there's a problem with the router. Especially if you're getting the speed you're paying for when connected via hardwire.