It could be hardware related (i.e..the connection) but more likely to be software... Do you have another PC you can test it on connected directly to the modem, this will confirm whether it's VM.. If not then add the router, then retest, then add your download manager and retest, then the firewall, then the AV...you get my drift
It's exactly how you modular check suspected hardware faults/conflicts, you drop down to the very basic needed to work then you add the bits from there testing after each addition