Yup... that's what I was getting at here. This is a common issue if you have devices connected to other APs or switches (beyond the integrated AP/switch in your router) since their connections will not be bounced by the swap of the routers themselves.
I'd recommend that you open a new thread for this topic, since now the main topic has been solved. This will help you get the right eyes on your speed problem questions and hopefully they can guide you to good solutions to improve the overall speed of your connection.
And in that spirit:
If your problem is solved, please consider marking this topic as [Solved]. See How to mark a topic as [Solved] for a short how-to.