I'm with Oly....something is preventing fluid from returning to the MC....
Either the tiny hole in the bottom of the reservoir is blocked, or the push rod is adjusted so that it is a tad too long and not allowing the piston to return to its internal stop in the MC, thus uncovering the return ports in the MC.
The brake pedal slapping back against the toe board is not really much of a guide- it'll do that with no MC at all.....disconnect the clevis yoke at the brake pedal linkage- if the MC spring pushes the piston & clevis yoke past the brake pedal arm hole, then the push rod is adjusted too long.
Recently had this problem with my '64 Valiant after a complete system re-build....turned-out that the pedal-arm mounted stoplight switch was preventing the pedal from returning all the way to "rest", and preventing the fluid from returning to the reservoir....same symptoms: hot wheels, no play in the brake pedal when warm.
A quick adjustment to the stoplight switch took care of this in my case....but the SLS shouldn't be part of your equation.
Also, you might have your shoes adjusted a bit too tight....check your MC linkage first...if the hot wheel/ dragging problem persists, then back off the adjusters a few notches at each wheel.
Good Luck!
