1 gig blowndown

Hello,
I am getting very low download speeds with the 1 Gigabit service. I have had this service for over a year now with no problems. I usually get in the range of 980Mbps, but lately I've been getting 127-360Mbps. I keeps fluctuating. I am experiencing being repeatedly kicked out of games online and voice problems to where others cannot hear me. they ir tests and were getting in the 980Mbps range, but my computer and laptop are both getting way lower like I specified. I used to get 980+ Mbps and for some reason I am not. They even did me a favor and swapped the modem out, but I am still getting these very low speeds. I am directly connected to the modem provided by Comcast for this service. I do not know what else to do. Any help?