I agree to try to flush it out. If it were me I'd start by removing the radiator hoses, T-stat(s) and coolant filters (if applicable) to see if you can purge it through both the radiator and engine block with a garden hose. If successful I would then do the same thing with heater core. After that I would try filling the system with water (leave the T-stat out) and start the engine for a short time. Keep flushing until you feel you have everything out and then follow Brett's (wolfe10) excellent procedure for changing coolant. He has posted it around here a few times and if you cannot find it I'm sure he will be glad to post it again.
Last point, before you do anything check the engine and xmission dipsticks for normal color and levels to be sure there is not something else going on and don't forget to replace the T-stat(s) and coolant filter (if you have one). Good luck.
Lou
05 Travel Supreme Envoy