I've heard of some problems happening with that modem and consoles, needed port forwarding. But iphones, ipads, computers are all supposed to work great with it so your problem is a little weird.
If those devices were working okay with a previous modem, and work okay with wifi elsewhere. then I say get the modem exchanged.
Actually before you do that, just take note of these things.
The modem shouldn't be in physical contact with any other electronic device, or within 1 foot of one. It should be at least a few feet away from things like speakers, and cordless phone bases/chargers. And it should be plugged directly into a wall outlet, rather than an extension/power bar.
Also, make sure it's connected to the original outlet it was installed into, moving the modem to another outlet without a tech can cause speed issues/internet connectivity issues to arise, as not all outlets are suited/configured for internet connections.
If all of these precautions are taken and it's still not working properly, then definitely go to exchange the modem.