I would suspect your internet adapter is degraded.
If you formatted and reinstalled everything from scratch, then that would be sufficient proof that you're not being affected by a corrupt driver or any other software issues.
Here's something for you to test. Disable your wireless internet adapter from the device manager and try using your internet service via ethernet cable. See if the problem goes away.
If not, re-enable your wireless internet adapter from the device manager, and then disable the ethernet adapter.
This should help you determine where the problem lies.
If while trying both alternatives the problem persists, then I'd look at something else. However, any other cause would be highly unlikely, I believe.