Shaking while Braking Mystery Continues....

So, I own a 2010 Mustang V6 premium with 20 inch wheels. It has 75xxx miles on it and drives like a Champ. It is also my daily driver and over a period of time I have noticed an increase in the steering wheel shake while braking. Higher the speed I brake more the steering wheel shake it was. So, I have done following till now and got following results so far:
1) As a rule of Thumb, I got all the 4 wheels re-balanced and it helped with removing the steering wheel shake due to wheel imbalance while driving from say 55 to 65 mph but didn't help steering wheel shake while braking.
2) Got all 4 new rites installed along with the Wheel re balancing. So, getting all 4 new tires helped with the steering wheel stiffness a little bit and the ride is now smoother, but didn't help steering wheel shake while braking.
3) Replaced all 4 brake rotors with Power stop Z26 performance rotors. And also bled all 4 brake lines like hell and used DOT4 brake fluid instead of DOT3. Largely reduced the steering wheel shakes while braking, So now, I didn't have any steering wheel shaking while braking below 50mph. But steering wheel still shaking while braking over 50mph.
4) Replaced all 4 Brake calipers with Power stop performance Brake Calipers. Did not help with anything.
Now, with all of the above parts replaced and putting in a **** Loads of Money and time in this stupid Issue, I still have Steering wheel shake while braking above 50mph. While braking below 50mph I feel absolutely Nothing at all. It does feel like my steering wheel shakes more while I brake lightly and does not so much when I brake with full force.

I recently got it Check from two mechanic Shops and one of them told me that there is nothing wrong under the Car, my tie rods and control arms looks OK. However, the second mechanic told me that my Lower control arm shows some signs of wear and I should try getting them both replaced along with the Ball joints.

Now, I am on the brink of Braking off....... It is hard for me to believe any mechanic saying anything. Please Help !!! Should I go ahead and get my lower control arms and ball joints replaced???

This is very frustrating for me to keep on putting more and more money over and ever again into the same stupid problem in a car which is supposed to be well built, while my 2003 Nissan has 140K+ miles on it and not even a single problem. Brake Pads are the only thing ever replaced on it and that's about it, oh and it brakes wayyyyy better than mustang. I feel ashamed of buying an American car. Please help !!!