I have a 2000 ford focus when it started to get cooler weather the car would decline in speed while driving and the factory radio won't cut off when shut the car off for about 2 min ok changed the thremostat and the fuel pump and housing assembly but the problem is still there what is wrong with my car

I think you have tow issues here that the dealer needs to scan the cars electronics to confirm. The radio problem is due to a sticking door latch switch that senses when the door is opened to shut off the accessories like the radio. The other problem with the way it runs can be understood by reading my explanation below.

The engine and the automatic transmission (transmission control is only for automatics, engine is still computer controlled no matter the transmission type) in this vehicle are computer controlled and in most cases when a fault occurs a fault code is stored in the memory of the computer control module. There are exception to this, such as the Mass Airflow Meter and fuel pressure problems. What must be done is to have all the basic testing done such as a scan of the system for fault codes as well as a check with a live data scanner tool for engine functions that are not within range of normal, a trained technician is required to know what is correct and what isn't, then based on careful diagnostics done from a factory repair manual the correct part is replaced or the wiring repaired or the computer replaced (known as the PCM or ECM,ECU), which is very rarely the problem. Other basic checks must be done as well such as mechanical problems with the engine as well as engine state of tune and mileage on the engine. The transmission can have mechanical issues as well such as no gear engagement at all or a failed pump or other pressure related problems. Also engine mechanical problems can and do cause many drive-ability related problem such as rough idle and other symptoms.