speed problems

I am thrilled to see that Xfinity is increasing my already in theory speeds.  Unfortunately my current speed listed at 800 mbps is only around 26 mbps in practice.  This is probably my fault for not bringing it up sooner since this really began when Xfinity repaired the line some years back.  I know that it is now suggested that i get a new router for the higher speeds but I am skeptical that the speed is a result of the router.  I am paying top dollar for the internet so I am not sure what the next steps should be.