So was going 50 in 4th (auto) and tapped the brakes and it shifted into 3rd then back to 4th when I took my foot on the peddle.
I just have to press enough to make the brakes lights come on and it will shift.
Brake lights on
shifts into 3rd.
Brake lights off 4th.

 

OK?

 

Are you sure it is shifting or is the torque converter coming unlocked? The converter will unlock when you let off of the gas or tap the brake.