I can confirm I have also experienced the drop in upload speed since installing the new firmware in my 8800AXL.
The following figures are from MDWS:
On 21/04/15, the last but one time my link dropped unexpectedly, I was connected at Upstream rate = 16429 Kbps, Downstream rate = 55695 Kbps
I did the "upgrade" the weekend before last, my download stayed roughly the same, my upload went from 16429 to 15934 Kbps.
In the early hours of this morning my connection dropped, and changed to Upstream rate = 12912 Kbps, Downstream rate = 54494 Kbps.
I thought I would try a resynch around 14:00 today, so disconnected the internet and powered the router off for about 15-20 minutes
On restarting, my connection rates have dropped again, to Upstream rate = 12396 Kbps, Downstream rate = 54049 Kbps. The downstream is a bit lower, but that's a significant drop in the upstream.
I'll need to try reverting to the previous firmware, if I can find it. Does anyone have a link?