I really need help guys!

I've been having brake problems for the past couple months and have changed both my front calipers twice now due to faulty ones. Just picked up my car today and the give off for the bad calipers is my brake pedal would get stiff, and that didn't happen. I was going up the street and had a hard time getting to 50mph and it felt like my car was dragging. When I did get to 50 I was trying to keep it there but it would keep shifting back to either 4th or 3rd to keep it at speed.

Got out to check the brakes and no burnt smells there so I ruled that out. Also, if I let go of the gas pedal to coast. It decelerates at a much faster rate than normal. If I could guess from 50 - 40 in less than 10 seconds of coasting.

My tuner said it could be my Brake Master Cylinder but I need some more opinions before I buy the part.

PLEASE HELP!!

 

To add on top of it. Drove to today and it was working fine for a while. On my way home the brake pedal started to get stiff again...

Thinking it could be the Brake Booster?

 

no one has any idea of what this could be?!