Internet goes out and back in irregular intervals

Hello! I have an odd problem with my internet where starting a few months ago (around March or April), the internet would randomly go out for about 5 to 10 seconds before coming back. The interval for which this happens is completely random. I've had it occur fewer than 30 minutes apart and at one point didn't have it occur for around 6 hours. This was on wireless, and here's what I tried to do in order, the problem still persisted:

Tested different phones and computers
Called isp, told me no problems were detected on the line
Power cycled the router
Moved the router into a different room
Tried a wired connection instead of wireless
Reset the router to factory settings
Made sure firmware was up to date

My router-modem is from CenturyLink, ZyXEL PK5001Z model.


Tech Support Guy System Info Utility version 1.0.0.2
OS Version: Microsoft Windows 8.1, 64 bit
Processor: AMD A8-4500M APU with Radeon(tm) HD Graphics, AMD64 Family 21 Model 16 Stepping 1
Processor Count: 4
RAM: 5588 Mb
Graphics Card: AMD Radeon HD 7640G, 512 Mb
Hard Drives: C: Total - 285810 MB, Free - 167439 MB; D: Total - 407423 MB, Free - 377081 MB;
Motherboard: ASUSTeK COMPUTER INC., K55N
Antivirus: Windows Defender, Disabled