I am getting my right front axel assembly replaced because of a vibration problem similar to what you are explaining. Shop said I have too much play in my CV joint and axel.

99 Black SVT -3L Hybrid w/.5mm overbore, Spec clutch/flywheel, MSDS, BAT intake, K&N open, 17'Konig Tantrums, DMD, Opt. TB & Y, Powerslots, Bassani w/ magnaflow res. 96 SE MTX- "The War Wagon" "I'm in love with my car..." -Queen