Godaddy does not have slow servers- I use them for all of the sites I build for clients, and their hosting is fast and reliable. However, if you are making demands on the server that exceeds the limitations of your hosting package, they will throttle you to prevent other customers from being impacted.
They have already told you that you are hitting their memory resource limit. So, you can either optimize your site or log on to your GoDaddy cPanel and increase your "Resource Level" to the next increment.
Go to Metrics and look at "CPU and Concurrent Connection Usage" to see graphs of your resource usage. If you are flat lined at the top of any graphs, your site was limited during the hours shown.
Why don't you give us your site URL, so we can give you specific suggestions on how to speed it up?