Wierd RPM Fluctuation and Vehicle shuddering

[brunetp]

Hey , Wondering if anyone can help me out.

When i'm driving in town 40-60 km/h and hold the gas pedal steady the Rpm will slowly fluctuate up and down about 100-200Rpm every 1-2sec and can also feel it in the car, And when i push the pedal down just a little bit to give it a bit of load the Engine/Car shudders until i let go of the gas or make it shift into a lower gear, It only does this at lower Rpm's after it's shifted into that 3rd or 4th gear in town. IT's perfectly fine on the highway.

Anybody have any ideas?? I replaced the Plug wires and the Intake Manifold Gasket which cleared up the rough idle and some of the worser shuddering and also replaced and gapped the Plugs, I've also done the timing belt, and it has a trany cooler.

I've replaced many things on this car so if anyone else has some Questions ask away.