1997 dodge dakota not heating up alot.

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replaced thermostat, tried flushing, new antifreeze, and the temp hasn't come up yet. While running I took off the small coming out of the firewall going into the water pump and there is a small trickle of fluid going through. So I assume heater core is clogged. Anyother way of trying to unclog system??? A new heater core is cheap but alot of work to put in taking dash off disconnecting AC lines. Dealer want just under $1000 to do the job. HELP!!!!!!!