The rocking back and forth I assume is the engine cutting out and giving you power, then no power, then power...
Since you just replaced the fuel filter, look there first. Its quite possible that you sucked a piece of dirt into an injector, the fuel pressure regulator, or the fuel rail. Its also possible that your fuel pump is dying but you've overlooked it since more recent modifications lead you to think that they are at fault.
Fuel demand is directly proportional to how much of your right foot is used. Try this. From a stand-still, floor it. How fast do you get before the problem happens? You mentioned that the problem happens at 80kmh and gets worse if you add more "foot."
If you are able, do the tests yourself, but this sounds like a classic fuel supply problem. Piece of dirt somwhere, bad fuel pump, bad fuel pressure regulator, leaky line... something is causing the injectors to not get the pressure or volume of fuel that they need. Let us know what you find out. As much as we educate you on this, it educates me/us knowing that we were wrong/right.
