Mystery Brakes: Smoking, Brakes to floor, spongy, smoking (again)

I was driving to the auto parts store in my 1989 Ford Ranger when I started smelling something that was either the clutch or the brakes. When I saw smoke coming out of the passenger side tire I knew it was the brakes. I pulled over and waited for the brakes to cool off. I tapped the caliper to see if it might loosen it. As I started on my way home, suddenly the pedal went to the floor. I pulled over and waited again but the pedal continued to go to the floor. I eventually got my truck home.
Since then I have swapped the master (bench bled before it was installed) and the booster. I also swapped out the rear brake wheel cylinders & shoes (the bleeder valve just came off when I tried to loosen it so I suspect these were on since 1989). Brakes were bled (2 person method).
The brakes were no longer to the floor but it felt spongy and not hard at all. I noticed a hissing sound when the brake was depressed (truck on). I swapped out the new booster with the old one and the hissing disappeared. Brakes appeared normal.
I drove it for about 5 miles before I started smelling the same thing I noticed previously. I kept driving and eventually pulled over after I saw the smoke again (this time it appeared to be coming from both wheels). I waited for about 30 minutes and tried to start the truck but it kept stalling. With the truck off, I pressed on the brake pedal a few times to release any backed up vacuum and then the truck started.
I drove the truck for another 15 miles without issue and got it home. I'm not sure what the problem is but perhaps it could be the caliper or the brake hose. Any ideas?

Issue was the brake booster. I drove around for a while until I felt the brake harder to press. Raised each front wheel separately. Both were very hard to turn. Loosed the connection between the master cylinder and the brake booster (1/8" to 1/4" separation). Rechecked raised wheel, turned freely. Separated the master cylinder from brake booster about 1/2" and wheel spun more freely. Replaced brake booster and repeated test. Both wheels turned freely.

so what I’m getting from this is the rod that pushes the piston was too tight and was already engaging the brakes before the pedal was being pressed. Am I getting this right?