What possible causes for suspension to shake and feel unstable above 50mph?

I have replaced all tie rods, arm bushings, ball joints and fitted new rims and tires. Balancing has been carried out too. Confused...

After replacing all that did you get an alignment? also this ais an all wheel drive vehicle, have you checked the front drive axles (cv joints) and after replacing the stuff was the axle nut torqued propperly? front wheel bearings could also cause shaking..