1999 Chevy Tahoe response

I have a 1999 Chevy Tahoe and im experiencein violent shaking in the fron end while driving any where from 30 mph and up. I've had the powersteering gear box replaced and the symptoms got worse. I have an appointment to replace both lower ball joints, both drive axles, and to have it aligned. The mechanic states that uppers and tie rod inners and ends are good. If after replacing these, i still experience violent shaking, what should i do next.