Slow speed issue - modem needs to be reset regularly

Please explain the scam.  I come home, reset the router that Comcast provided, and have reasonable internet speeds for a few hours.  By the next day, my internet speed is at a crawl and I need to go reset the router, again.  I paid for very fast internet speed, but it seems that Comcast cannot consistently provide such speeds to all of the customers that paid for such service.  Is this why the router must be reset all the time?  I've had Comcast out 3 or 4 times and they always apologize and provide different equipment.  The service is fine when they leave, but then I am back to the old hassle.  Reset the router all the time, or accept internet speeds that are a fraction of the service for which I paid.  If Comcast sells a product that they are unable to provide, and then provides routers that could be configured to reset on their own when service is poor, yet they don't do this, is Comcast not in fact asking its customers to file a class action suit?