universal joints and even your drive shaft can cause a slight vibration. The fact that you said it happens around 50 mph would normally tell me you have an unbalanced tire, but as you said you swapped them. Something you might want to try if you havent already is rotating the fronts to the back, to eliminate a bent rim. Just curious because I am not sure of the exact part names, you said you already changed your wheel bearings, and CV joints? They too can cause vibration. There are plenty of other issues that can cause vibration, from improperly installed CV joints, over/under tightened wheel bearings, mounts gone bad or broken, to just simple rust that might have got onto the rotors. Some more information might pin points your issue, such as does it go away at higher speeds? Does it do it when the roads are wet? Have you tried rotating your wheels from front to back? Did you replace the front end parts because of the vibration or did it start after you replaced those parts, and lastly are you running stock suspension, or lifted/lowered?