I HAVE A PROBLEM WITH THE BRAKES ACTING LIKE THEY ARE APPLYIng WHEN SLOWING DOWN, IF i give gas then it disappears until I let off again.

 

What year Mustang are we working on? Are those factory power drums? and, has any work been done to them recently?

 

1968 coup as far as I know factory power drum but I just bought last November and this is the first time I drove after doing major work to the body and floor boards.

 

There are actually more possible things to go check when there are aftermarket parts installed. I am not aware of a go-to problem for factory power brakes. Drums, when they have problems, typically also provide unwanted directional input. You aren't experiencing any unwanted steering input when you use the brakes? Or are any of the rims hot to the touch after driving? Does the feeling that the brakes are applied go away if you coast with the car in neutral? If that was the case, I would say you have tall rear end gears. Even 350:1 gears will create a good bit of engine braking.