Strange speed problem - download slowing upload

[MaFi0s0]

I have only 1 active torrent which is seeding to 1 user at 70Kb/s, in this torrent there are no other seeders and no other active peers, so no external factors.

I then start to download another torrent, this torrent begins to download at any speed, in this instance although it doesnt effect the problem, I have happened to cap the upload speed of this particular torrent to 9kb/s.

The seeded torrent upload speed will drop to 20-30Kb/s

uTorrent is capped at 90Kb/s up.

My internet speed is 30MBit down 1.15Mbit up (128Kb/s)

Running speed test while utorrent is active I get 30Mbit down 0.9Mbit up.

I am using:

Windows 7 x64

Cable internet

Motorolla SB5101 modem

D-Link dgl-4100 router: SPI off, DMZ is enabled.

AV is Kaspersky with Web AV disabled and Firewall disabled. Although Network attack blocker is enabled.

I have tried:

disabling bandwidth management

disabling uPnP port mapping which works fine either way.

setting bt.tcp_control_rate to false

changing net.max_halfopen from 40 to 4.

changing priorities of the torrents which dont seem to work

checking "seeding tasks have higher priority than downloading tasks" which doesnt seem to work

disabling network attack blocker in Kaspersky.

changing bt.transp_disposition to 5 from 15

disabling DHT

What is strange is if I pause the downloading torrent the seeding torrent goes back to 70Kb/s but then as soon as I unpause it even if it is at a really slow speed like 5Kb/s up and down the seeding torrent drops to 25Kb/s.

Also if the 2nd torrent is one I am seeding, my total upload speed will remain the same or go higher, in other words it only seems to be either large swarms or torrents I am downloading that effect my seed speed, by individual torrent bandwidth priority wont work, for example if I want to seed one torrent at 70Kb/s and another at 20Kb/s rather than ~45 ~45.

If no1 can provide a quick fix and a mod/dev has interest I will go into a lot more detail on specs, settings etc.

[DreadWingKnight]

What are your settings from preferences - bandwidth and preferences - queueing currently?

[MaFi0s0]

Bandwidth:

max up: 90

alt upload rate when... unchecked

max download rate 0

global max number of connections 450 (while having this problem I see about <50 connections in uTorrent)

max connected peers per torrent: 100

number of upload slots per torrent: alt between 1 and 6.

use add. upload slots if upload speed < 90% is checked.

Queueing:

max number of act torrents up and down: 6

max number of active downloads: 5

ratio is <= 200% ....... 0

seeding tasks have higher priority alternate between checked and unchecked

when utorrent reaches seeding goal checked and 0.

everything under adv is unchanged unless mentioned earlier.

[Switeck]

Try setting bt.tcp_rate_control to FALSE.

And if seems to have no effect over 10 minutes, disable uTP (uncheck bandwidth management in Preferences, Bittorrent).

...You may just have too many connections on the other torrent/s!

[MaFi0s0]

I have tried both of these things and together for the past few hours.

By the way I can confirm this problem is not happening in Vuze.