[Solved] Bad Modem or Router?

Ok, the internet at my house has been turning off for 5min or so randomly and then coming back on and when it does this nothing shows up on any of the computers in the house that I would suspect with a bad router such as "local area cable unplugged," or "this network has limited or no connectivity." I have called my ISP and had a tech out a couple of times and as far as they can tell everything is fine on their end. I swapped out the router with a backup one I had and tested the DL and UL speeds and they did increase, but the internet still seems to drop out once and a while from heavy and/or constant usage such as gaming or downloads. So my question is, does this sound like the modem is going bad? Is there anyway I can test my modem?

I did do a smokeping for 48hours through DSLreports and my ping stayed fairly constant with the exception of one random spike.

Thanks in advance and please let me know if you need more information

Thanks for the reply, it ended up being the modem, but the router isn't far behind, the wired is fine, but the wireless drops in and out.