[dsraven]

a better description of your system would help but if the pedal is slow to return then the first thing I would check is the pedal pivot to ensure it is free turning. disconnect the pushrod to the pedal and see if it swings easily and returns to the top without dragging. next up I would check all the linkages and pivots to ensure nothing is binding or rubbing on something that may move with body flex. next check the pushrod free play at the master cylinder, you need to have free play so the piston in the master cylinder can travel back all the way and allow the fluid to return to the res, especially if you notice the brakes only drag after they have been heated up. with not enough free play the fluid in the system heats up, expands, and then the brakes drag because the fluid pressure can't escape back to the reservoir. if you have a bunch of linkages before the master cylinder then it could be that theweight of all the linkage and pivots etc is hard for the master cyl to overcome. a simple return spring on the linkage may fix the issue.
is your system a frame mounted system or a firewall mounted system? disc all around or disc front drum rear? are you running residual valves in the lines? do you have free play in the pushrod at the master cylinder?