my 99 2.5L still has a fluctuating temp gauge.... i replaced the sender,the sensor , thermostat, i flushed the radiator ( the coolant was real dirty an dark) ...so after all that the temp gauge is still fluxuating an the heater should be alot warmer than what it is.... DO I NEED TO TRY FLUSHING OR AIR BLOWING OUT THE HEATER CORE?

 

Using air to blow out the heater core could lead to a leaking core. They aren't really made to withstand high pressure. Best bet is BACK FLUSHING the core with a garden hose if you think it is plugged. However, I am thinking you may be needing a new water pump. Just a guess based on what you have done thus far.