Hey guys I'm stuped on this one...

I have foam in my radiator, and when I shift and the truck comes down on RPM's the water temp goes full tilt (I think it is reading air or gas temp for a split second, then it goes to normal).

It dosn't seem like the water pump because I am not overheating and am still getting flow through the system when the motor comes up to temp (at the same time though I am getting bubbles) I think it Could have somthing to do with the water pump seal or did I loose a head gasket? Also how would I tell the difference between these two sceanarios? and why the hell is my water temp gage going haywire like that

Thanks for any help in advance,

Big John (motor rookie)