Comcast increased speeds not decreased them
Comcast increased speeds after they took over ATTBI not reduced them. When AT&T transferred customers from the @Home network to their own network the maximum download speed was 1.5. After Comcast took control they raised the speed to 3.0.
I do not know what Comcast did out side of Pittsburg, CA. But in my city they reduced speed. We were already getting 3 Mbps before Comcast took over. For the first nine months our speed was cut in half. It then picked up to 4 Mbps.