but it is still exceedingly slow and limited when it comes to changing the channel, or using the internet at the same time.
Actually I'm not sure if you can get their High Speed Plus when you have HD??
At any given moment there are 3-4 tvs in my house on at the same time + light-moderate internet usage. I don't like the idea of knowing that I am paying for a service that I can't use, you shouldn't have to baby your service (i.e keep your other box/boxes off so that you can watch hd on your main tv)
Actually in my case upgrading to High Speed Plus seemed to solve all my HD issues. When I had High Speed Classic they insisted that both tv and internet could be handled by the same line, even though heavy internet usage obviously had an adverse affect on the TV. When I upgraded to High Speed Plus they ran a second line into the house, so now TV and internet are on completely separate lines and handled by two different modems (also, there is just the one TV in the house, so the line is completely dedicated to that TV). I'm not 100% certain that this was the only factor in fixing my problems, since the tech said they were working on some kind of line issues or something at the same time, but it's probably worth looking into.
Of course you shouldn't have to pay for High Speed Plus if you don't really want it, but maybe they would run a second line anyway if you pressed them on it?
It really seems like they have the ability to reliably send a single HD signal over the line but no more.