For hydraulic brakes that are dragging or slow to release it could be a number of issues. If you have used the wrong type of fluid required by your brake set up, that could cause the problem. There may also be a foreign object in the master cylinder blocking the correct flow of fluid. For either of these you will need to drain the system, check for foreign objects and remove them, flush the system and refill/bleed the system using the correct brake fluid.
If your system has a parking brake check that it is functioning properly and can move freely.
If you have drum brakes, make sure they are properly adjusted. Also make sure you are using a drum actuator for drum brakes or a disc actuator for disc brakes.
If the system has a breakaway kit, make sure that there are no broken or corroded connections in the wiring and that the battery is fully charged and the pin in the switch is all the way in.