C3000/N300 Speed and Range WiFi Cable Modem Router

Recently purchased a C3000|N300 Cable Modem Router with 25 Mbps xfinity cable internet but have a few questions

• Can someone confirm that the C3000 is NOT dual band? documenation shows that it can have 5 ghz or 2.5 ghz, and I've set to 2.5 both for the increased range (we've had so many issues that we've had to purchase a range extender) and device compatibility but I just wanted to confirm that I can't have both
• Our internet is just INCREDIBLY slow - I hit the promised 25-30 Mbps wired but the wifi speed even sitting next to the C3000 I only get 1-2 mbps download and ~1 mbps upload. Is this typical?
  • If this is in fact typical I'm looking for router considerations - should i replace the C3000 altogether or just purchase another router? If so may I please have some recommendations on model? we're in a 2k sq foot 4 story townhouse and we've purchased a wifi extender, the C3000 is currently sitting in our 2nd story

Thank you in advance for any help/advice provided!