I will say they have been great to work with on customer service-I know dont say it yes att&t customer service is great-yes with me they have been. Cell plans should get cheaper overall I know wishful thinking.
I don't think ATT is going to upgrade anything until the TMO buyout goes through, because as you said and in my experience ATT's dead zones are covered by TMO.
Or the buyout doesn't get approved and they have to upgrade on their own.
Just to give you comparison in my area... Sprint and Metro PCS give the best voice coverage followed by Verizon, T-Mobile and AT&T...in that order.
I'd be willing to guess that AT&T doesn't let the speed go as fast as it can so people don't go over their tiered data plans as fast.
That's my personal theory, I'm not sure if it's right or not. -shrugs-