Answers follow.
Internet Service Provider and Modem Configurations
What ISP Service do you have? Cable or DSL? - Cable
What ISP Modem Mfr. and model # do you have? Motorola SBV5121
Wireless Configurations
Links>Wireless Installation Considerations and Managing Signal Congestion and Good Neighbour Policy - Ok, took all actions.
Ensure the default (dlink) SSID name is changed. Ensure that different SSID names are used between each WiFi 2.4/5Ghz radios. Can be anything and not something that's already in use by any neighbouring WiFi routers. Under Setup/Wireless/Manual. - Ok, took all actions.
What wireless modes are you using?
2.4Ghz Routers only: Try single mode G or N or mixed G and N? - Changed to mixed G and N.
Channel Width set for Auto 20/40Mhz or try 20Mhz only. - Changed to Auto 20/40Mhz.
Try setting a manual Channel to a open or unused channel. 1, 6 or 11. 11 for single mode N if the channel is clear. 13 for EU regions. - Channel changed to 11.
What security mode are you using? Preferred security is WPA-Personal. WPA2/AES Only. Some WiFi adapters don't support AES, so you might want to try TPIK only or Auto TPIK and AES. - Changed to WPA Personal, WAP2 only and AES.
What wireless devices do you have connected? - 2 Laptops and 2 cellphones (iphone and motorola)
Ensure any devices with WiFi adapter drivers are updated. - Updated
Any 2.4Ghz or 5Ghz cordless house phones or WiFi APs near by that maybe causing interferences? - None
Any other WiFi routers in the area that maybe causing interferences? Link> Use a WiFi Scanner to find out. How many? Only one from neighbor, but in another channel.