If AT&T is shaping traffic, it is a very new process. I had DSL from February, 2001 (when it was offered as, "Pacific Bell DSL Service" through April, 2011 (when it was, "at&t Yahoo! HSI Pro"). I never knew them to "shape" traffic. I've run both "glasnost"
on that line with no evidence of traffic shapers.
I have been with another ISP since April, 2011, and can't test an AT&T DSL connection at present.