C3700 - Suddenly Slow

My internet has recently been significantly slower (terrible speeds on speed tests, etc.) at random times. I contacted my ISP, Comcast; they performed some trouble-shooting steps, but eventually told me that it looked like the problem was on the modem end.

 

It's not always the same, but it's happened with regularity; I show as having full internet connectivity, but the speeds are significantly slower. This repeats regardless of whether I'm on Chrome or Firefox; indeed, it often seems to make whichever browser I'm using runs with far more energy than is typical, heating up my laptop. If I try using apps on my phone or tablet they often experience delays or interrupted connections on wifi; switch to cell service, and it's fine (even though the cell is often only 1-2 bars at my home).

 

I double-checked, and the router firmware is up-to-date; I unplugged everything and made sure no dust or debris was in the way of any cords or cables

 

* No additional devices have been using the router

* I don't have cable, phone, or security services connected

* As far as I can tell, nothing should have changed the behavior

 

I guess the moral of my question is - is there anything I can do here, or do I just have to live with it? My router is definitely out of warranty; I've had it at least since I moved to this apartment over 2 years ago.