We still need more information than what you have provided to really provide any real educated solutions. First you said that you changed the trackbar and pitman arm, then you said you have not??
Any time you have shaking you first need to get the wheel's balanced well, make shure they are balanced and wheel's are not bent (try rotating also).
Also make sure that you have a good alignment and your castor is within a reasonable amount for a 8" lift (you will have to check with others on the castor setting for that high of a lift).
After these two things have been completed there is a long list of other remedies including but not limited to: Trackbar, Ball joints, TRE's, bushings, etc, etc, etc.
Michael