instead of setting fire to "bad ************" that was owned by Sam jackson in pulp fiction, first do a fluid and filter change, your car should be having an electronic control transmission, the shift points are decided by the TCU which takes input from, the speedo pulse and the throttle position sensor on the carburettor.
The TC on these trans can go out, but that is usually due to overheated transmission, btw what is the operating temperature of your engine? and when was the last time you changed the fluid?