vibration while in the gas

I have a 95 LeSabre, and while I am in the gas my car vibrates. I notice it most around 50 mph. It completely goes away when I give it full throttle or when I completly let off of the gas. But when I am driving normaly ( regeular accerlation or steady speed) it vibrates. I notice it between 35 and 80, but like I said, it is most noticeable around 50mph. I have cleaned the throttle body and it help a little bit, but the problem didn't completly go away. Any Ideas????

Time for a good tune-up, wires, plugs and check the coils. Sounds like secondary ignition misfire.

Yah.. I agree.

Ive tested plugs under pressure, watching through a glass window.. saw how they quit under different pressures.

Good Luck