Test Results

I am concerned with how at some times the speed is well under 1MB and others it is around 25MB or anywhere in between. The tests were conducted on testmy.net but I get similar results with different speed tests as well. I used many different devices at many different times. It did not seem to make much of a difference if they were wired or through wifi. I have the triple play package and am pretty sure I should be getting 25 down/5 up. I am wondering if it could be the modem, a bad connection, too much traffic, or something else. I have an Arris TG862G supplied by comcast that has been switched out multiple times because of connections constantly dropping and different reps saying it has to be the modem. I have heard some mixed opinions about this model. What do you guys think could be the problem and do you have any suggestions? I understand that it is pretty much impossible to know for sure based on the little information that I have given but just wanted some opinions. Thank you in advance for any opinions or suggestions.