I'm also in the Tri-Cities and have noticed in the evenings the last few weeks the speeds have been in the 3-7 mbit range. I've done the same as you and all my signal levels seem to be in acceptable ranges. My guess is that since more people are on the 30mbit and 100mbit plans the nodes in the area are starting to peak. Hopefully Charter is looking into this.
Happening again tonight when I went to update Mac OSX. Was SHOCKED when the 400Mb download was only 40% done after like 5 minutes of me leaving to get something to drink. I'm used to amazing download speed especially when pulling from Apple servers and updates of any size taking no more then one or two minutes. I've loved Charter's speed and hopefully this isn't a "new level of acceptable" service and instead an issue on the backend or backbone's being changed... I posted in Charter direct just now about it and I suggest you do to to show there is an issue, even if sporadic.
This is poor speed even for a 30Mbit plan (I would hope at least 10Mbits during peak) but for 100Mbit plan it's laughable. Getting only 7% of advertised speed points to a real issue...
It's funny, Frontier just recently in the last couple weeks started leaving door hangers and mailers about how their DSL speeds in this area have been upgraded considerably and they're "far cheaper" then what cable internet charges... I would hate to give up 100Mbit Charter but if I could get 80% of even a 30Mbit DSL plan 24/7 for less then half the cost, it might be worth it...
I can't remember how much the internet price of the package is but I wanna say it's like $90 or something for Charter's 100Mbits, so ok, maybe not completely half, but I think Frontier has some really great promo right now for the first year or something.