Front Brake problems HELP!!!

Since ive had this car its front brakes(4 wheel disc) have dragged sometimes and sometimes much more than others to where the calipers dont release all the way. Initially it got to the point where it burned up my whole front brakes. So ive replaced the front calipers, master cylinder, brake hoses, and the proportioning valve. Ive regreased the slider rails incase something was sticking. They dont lock or drag all of the time. After the car sits or cools off they usually release. Then I start driving again and after a few hard stops they start sticking and the pedal gets very firm and my brakes heat up. And when they do get locked it can get to the point where at idle in drive the car either dosent move forward at all or just barely moves. Heres another weird thing, if I take the car up to about 110-120mph and then slow down the brakes are free again for a little while but its got to be up around that fast maybe 90-100mph. Im at my wits end and dont know what to do with this thing. Could it be that the booster isnt adjusted right?

Heres a sub question about my brakes that could have to do with my problems. My front brake calipers are regular iron calipers. My rear brake calipers are aluminum and have fins. Also the rear rotors look bigger than the fronts. Do any of you guys have iron front calipers and rear aluminum calipers?

Check to make sure the push rod that activates the master cylinder is not touching it before you press the pedal. There should be a little (.125 inch) free space. Some are adjustable and I had a car where the previous owner set it to where it was slightly activating the master without any pedal input, probably to try to make up for a bad cylinder. The symptoms were as you described. (except I never tried to go 100 mph while having brake problems, lol)

I get frustrated at times when this acts up and just gas it and it happened at a stop light that led to a onramp to the highway and i just nailed it and when i looked down and realized i was goin 120. Then when i went to slow down the pedal depressed as it should and all was well till i got back to normal stop and go traffic. Like i said the firmness of the pedal changes when it acts up. Would a bad booster do this? Maybe a vacuum problem with the booster?

check valve would be my first thought.

binding calipers would be a close second

check valve? .....theres another valve somewhere? or do you mean the proportioning valve? Because i changed that out. And how could the calipers bind? I regreased the slide guides...Since its both front brakes its gotta be something before them. Unless the rebuilt calipers I got are bad. Could the booster be totally bad? Im gonna get out there and check the rod to see if its pushed out too far. I didnt know that they were adjustable.

there is a check valve on the brake booster for vacuum, that way only engine vacuum is applied to one side of the booster diaphragm which is how it works. As far as the calipers binding, if the piston seal is bad, that's how it will bind, the seal acts as a return spring, so if it does not have it's original shape or is dry rotted it won't allow the piston to reseat and hence bind up.

hope that helps