My roommate works in retention at TWC. GP can definitely call and get that cut quite significantly. GP may not even have to threaten to leave -- just ask them to see if any promotions are available for that area. If they don't or don't offer enough of a discount, then threaten to cancel, get transferred to retention, and likely get an even better rate. The reps definitely have limits in what they can cut you down to, but $173/mo for basic cable and the 30mbps connection is pretty far from what they can get you down to.
http://imgur.com/rIrcxmJ