HELP! Strange network glitches: low b/w, erratic connection

Beginning Mid-December, my network has been acting with so many problems that 5 weeks of troubleshooting, repair, replacement and several ISP visits cannot help and I've exhausted my tech abilities and now I'm coming to you all for help.

[[Symptoms]]
- Bandwidth for several computers, wifi extender and even my iPhone range from 0% to 40% when previously they've experienced 100% while other computers still have 100% bandwidth; this is checked via Speedtest.net
- Random kicking off of wifi
- Computers connected directly to router with ethernet cables still have 100% of bandwidth
- First few weeks saw random drops from wifi several times a day, last few weeks saw constant low bandwidth with fewer drops from wifi still occurring
- PC that was brought clean during the holidays experienced same problem; since has returned back to their home and now that PC and those on their network are having the same problem

[[Attempts to Fix Problem]]
- Switched out Laptop Hard drive with another laptop hard drive; same problems occured
- Replaced the MODEM, replaced the ROUTER several times from different brands (belkin, netgear, d-link); no change
- Returned to original Belkin N+ Wireless Router and performed Factory Reset; no change
- Performed Antivirus scans with Windows Defender, Microsoft Security Essentials, Malwarebytes Anti-malware, Panda Security Cloud Antivirus and AVG Internet Security and PC tuneup; no viruses were found other than suspicious cookies
- Uninstalled, removed and reinstalled wireless card drivers; no change
- Uninstalled Java and internet explorer 10; no change
- Performed Registry cleanup; found 700+ errors, worked for a day, problem returned. Attempted Registry cleanup again, no errors.
- Checked each device connected to the wifi, each one alone with router; problem continues regardless of who is connected to wifi and ethernet at one time.
- Ping & tracert tests over 24 hours only confirmed which computers had the problems and which did not.

[[Devices affected]]
- 2 custom built PCs, each with Windows 8 Professional
- Gateway MT6705 with Windows 7 Professional and Internet Explorer 10 (since uninstalled)
- VIZIO Smart HDTV E320i-A0
- Apple iPhone 4S
- HTC Evo Shift 4G
- Netgear WN2000RPT Universal Wifi Extender connected to Xbox360
NOTE: all above are under Central Florida Bright House Network except for 1 custom-built PC which is currently under Comcast

[[Devices not Affected]]
Asus G1S notebook pc

What had the most promise was cleaning the registry but it didn't last 24 hours. What bothers me the most is that this is something that is also affecting the smartphones which should not able to gain a virus, IF what is affecting the computers is a virus; I say this because even with all computers off, the phones are also affected even if the router and modem has power-cycled.

Please, I'm at the end of my rope.

Please.

Help.