Mitsubishi Repair: vibrations, mitsubishi marage, balance shaft

Question
2000 mitsubishi marage, new tires up front, balanced all 4 tires and just got front end allignment. I get alot of vibration at 55-60mph and gets worse the more gas i give it, Drives very smooth up till about 55. What would cause this. Also the vibration decreases at high speed when I take my foot off the gas

Answer
Andrew,
This may be a caused a bad rim.  When a tire goes through a spin balance machine, they usually spin it the equivalent to the tire going about 30 MPH.  So its possible rims are slightly bent and even the balancing does not correct this.  There's also a possibility that harmonic balancer or balance shaft has a problem.  Even more common cause could be a worn or broken engine mount.  This may explain when taking your foot off the gas at high speed smooths out the vibrations.  Have your mechanic check those things if they haven't already.
Good luck!