Thank you for your suggestions of disabling QoS and DOS.
I have a newly purchased 2860 which is connected to a 100/30 leased line and following your suggestions I have increased the upload speed from 1.0mb\s to 29 mb\s as measured on speedtest.net..

In reply to a post by MarkatLangstone:

Thank you for your suggestions of disabling QoS and DOS.
I have a newly purchased 2860 which is connected to a 100/30 leased line and following your suggestions I have increased the upload speed from 1.0mb\s to 29 mb\s as measured on speedtest.net..

But was it DoS or QoS that fixed it?

QoS is very CPU intensive so could be the cause of your issue, but clearly wasn't the OP.

I had the same issues with a 2830n and QoS was to blame. The defaults on WAN2 (PPPoE) were Bandwidth: 10000Kbps/10000Kbps, Direction: Outbound, Class 1: 25%, Class 2: 25%, Class 3: 25%, Others: 25%. I disabled QoS and upload speed immediately went from 9Mbps to 19Mbps. Thank you very much Pipexer.