Is your Comcast DVR/Cable Box slow to respond to inputs from your remote? Did you already try changing the batteries in your cable remote control?
Before you try getting a new cable box from your cable provider, try unplugging your cable box from the power to reboot the whole system. It will take a minute or so to reset, but once the cable box is back up, it should be more responsive.
The cable box is basically a computer that will need to be rebooted from time to time to clear out dead processes and refresh the system. It’s just like any other computer running an operating system, in this case the cable box is likely running some form of embedded linux, it can begin to suffer from slow response times after running non stop for a long period of time.
Your cable box can also become slow it is left on constantly and overheats. So be sure to switch it off occasionally and give it a break. Maybe go outside and take in some fresh air.