Ok so if you are spiking every few mins or seconds this tut should fix most cases.
All credits to Cast on GunzFactor :
Note: This will not fix a sudden hike in pings, this will only help you if you have the type of spike that makes people 'freeze' for a short time. Wireless Routers only, of course.
Windows XP: Start > Run > Type in 'services.msc'
It should look like this...
Click the OK button, which will bring up the following dialogue.
You may want to maximise the screen. Scroll down to Wireless Zero Configuration and open it.
Once opened, you should see the following image:
Click the 'Stop' Button. Change the 'Startup type' from Automatic to Disabled.
Click OK. Voila, start GunZ, no more spiking.
For Vista users
This is easy...
Simply download the following program, and have it open whenever playing GunZ, or any other game for that matter.
WLAN Optimizer .NET, you can download it here : [Only registered and activated users can see links. ]
To prove it isn't a virus or w/e, I'll prove to you I have it.
NOTE: This MUST be open whenever GunZ is running, or you WILL spike. Also if you are using Windows 7 use the same technique as the vista version.