Brakes overheating after driving a while

Hi,

I am new to brakes so please bear with me. I have a 74 dart sport I just bought and it is having brake issues. It has power brakes with single piston discs in the front and drums in the back. I believe the brake system is all stock.

Here's whats happening:
For the first ~10-20mins of driving the brakes work fine with no issues. But after that they start to "stick" or for a lack of better words they slowly start to slow down the car until engine power just wont move it anymore. I have been stuck on the side of the road multiple times due to this. I've had to wait about 30 mins for them to go back to normal and even then the same thing happens after a few mins. Not fun. Theres usually a good abount of smoke coming from the front wheels as well.

I've replaced both front calipers and pads but that did not fix the issue. Any suggestions on what I should check? Or maybe I should just take it to a shop.

Thanks