It's best to run 3 batches of speed tests at different times of the day.
Also, please explain what you mean when you say you're losing connection. Does the signal completely drop? Do you get an error message? How often does it happen? What are you trying to do when it happens? Is it just surfing? Email? Streaming?
When the issues happen, what is the modem's state code? To find it out, go to this modem's page: http://192.168.0.1/#!/home/status and post the number next to State Code.