When I was on AT&T U-Verse they did this with torrents. I replaced my router, OS, and modem thinking the problem lay somewhere on my end, and once I ruled all of that out I called up AT&T to complain and call out the fact that it happened only when I torrented.

Their response was that yes, they do disrupt all torrenting traffic, "because it is illegal and they must comply with copyright holders". Nevermind it was various linux distros I was trying to download and evaluate, all torrenting is automatically evil by association.

I had to switch to Cox because they're the only other option in my area. The 250GB data cap on my plan is BS, but at least I can spend that 250GB however I please.

I had problems a while back with any long-running downloads or streaming video on ATT DSL. Basically made some uses impossible - any large remote data that couldn't resume at arbitrary points. Went completely away when I switched to a third-party ISP - using the same ATT-owned DSL lines.

I signed up for a VPN service right at the end, and that cleared everything up for me and completely confirmed they were intentionally shaping and disrupting traffic.