Bad service

I've got a weird lag on my Warlock, when I play BGs on it and someone caps a flag I get a 5 sec lagspike, this also happens in arena but not when I'm in Orgrimmar/raids etc.
This lag only happens on my warlock and not on my other characters (DK, Priest)

I've the problem on both my PCs, and I don't play with any addons.

Operating System:
Windows 2.6.1.7600
CPU Type:
Intel® Core™ i5-2300 CPU @ 2.80GHz
CPU Speed:
2.82 GHz
System Memory:
7.98 GB
Video Card Model:
AMD Radeon HD 6850
Video Card Memory:
743 MB
Video Card Driver:
aticfx32.dll
Desktop Resolution:
1920x1080
Hard Disk Size:
915.79 GB

I've downloaded all the latest drivers for my graphic card, network card and so on.

1 month and 6 tickets, yet my problem is not solved. All Blizzard do is talking rubbish, saying there's something wrong with my connection/PC. But I don't see how the lag is caused because of my PC when I only lag on my Warlock?

Please help!