Can't download HTC RUU for AT&T M8.

[sal2726]

OK. I bought a HTC M8, carrier branded with AT&T just to play with. Running 4.4.2 out of the box. AT&T shows no update available to push to me (even though I know 6.0 has been released). Trying to download the HTC RUU for Marshmallow, and it lets me get to the point that it is sending... Then just stays there. I have done it in fastboot USB, allow USB debugging, etc. Called HTC, they say you can't skip updates. Download 5.0 first. Tried that. Still stuck on sending. Any ideas?