drive line vibartation
 

installed a 3.5 in rough country lift on my 1997 grand Cherokee Laredo with 31x10.50 tires ,had front end alinement and still have a vibration even with new u joints ,what would cause this.

Try taking one end of each driveshaft off, turning them 180*, then bolting them back on.

Its a small lift so this may not be it but check your rear pinion angle.