Hi,
I have this remote with no problems. The first thing that I would try would be some NEW, FRESH, batteries that are high quality in the remote. Get some new Duracell's in there or something. When Spectrum gives out the remotes, you don't know a lot of times how fresh the batteries are.
With fresh batteries, you should be aiming the remote straight at the clock on the box and slightly downward. Back up about 4-6 feet for best results. With fresh batteries, and for a long time afterwords, I can aim my remote from straight across the room, or close to that. The lighted buttons should be bright when corresponding buttons are pressed. Remember, point the remote straight at the clock, and slightly downward.
If new batteries do not work, it is possible you may have a bad remote. You can call Spectrum and they will send you a replacement. You could also go online to look for an alternate remote, but there is no guarantee that it will work with Spectrum's cable boxes.
Actually, I would try new fresh batteries first before doing anything else. In fact, before you call Spectrum for a replacement remote, I would contact them for a signal and drop line test, (If new batteries don't solve this.) The Arris 3510 is a very good cable box, but there may be a signal or line issue causing problems with commands to the box.
Do not reboot any Spectrum equipment for six hours prior to your service appointment. This resets the error codes and the tech needs to see them. The service call is free and the tech should even have a new remote for you if that is the problem. Just say, "My box is really slow and sluggish even after new batteries in the remote. I would like to schedule a tech visit for a signal and drop line test." Get a service call if the new fresh batteries do not solve this issue. We need to check the drop lines and signals to the box to see if that is the problem.
Satch