Did you make sure its not just the thermostat?
-Disable air bag system.
-Drain engine coolant. Remove heater hoses at core, and plug core openings.
-Remove instrument cluster trim plate. Move tilt steering column down (if equipped), set parking brake and move automatic transmission gear selector to low (if equipped).
-Remove left underdash hush panel. Remove Data Link Connector and Remote Keyless Entry module connectors. Remove center underdash hush panel. Disconnect park brake release cable from instrument panel. Disconnect park brake cable from ratchet mechanism.
-Remove right underdash hush panel. Remove lighter and accessory outlets, if equipped. Remove courtesy light. Remove knee bolster. Partially pull A/C-heater control panel and radio to disconnect connectors on back of A/C-heater control panel and radio.
-Remove 4 steering column retaining bolts and lower steering column. Remove speaker and defroster grilles. Remove 9 instrument panel support bolts, including brake pedal bracket support bolt. Remove electrical connectors. Remove instrument panel.
-Remove core cover attaching screws. Remove retainers at end of core. Remove heater core. To install, reverse removal procedure. Fill cooling system, and check for leaks.