I am sorry ATT did not work for you, but if your really having a issue. Don't just sit there and wait for it to be fixed. I know when I got my Droid razr back in 2011. If I just let it be. I would have had 4 hour battery life, 4G that does not hold and when it did it would run at 600kbs. Call's droped and over heating.
I have never seen under a 1mbs on AT&T 3G before.( I have had over 4mbs most of the time and up to 12mbs max on the download.) With Verizon 3G Avg 300-900kbs DL. I am not seeing that kind of slow down with verzion 4G LTE and I live in one of the first AT&T and verizon LTE markets. So I think your iphone may have a 4G issue.
If you keep on having the issue. Then you should make a video and upload it to youtube.
P.S Good luck, hope it's better than mine was at getting any issues fixed.