GMC Repair: Heater Core, coolant system, temperature gauge

Question
I believe my heater core might be damaged or has a leak in it.  So, here's the vehicle history so that you may be able to help me solve my problem.  I drove from northern California and up until I got to Tennessee, I've had no problems with my Jimmy.  I am also towing a hitch behind my truck and it's a six cylinder.  Anyway, everytime I hit an incline the rmp will go crazy and my temperature gauge is still at 195-205 degrees.  The radiator is full of coolant, but the reservoir is guzzling the stuff up like it's water.  I checked under the vehicle to see if the hoses are leaking, but I didn't see anything to indicate that.  I can smell the antifreeze and there's steam coming from the vents.  Is there a temporary fix to this problem so that I may drive my vehicle where I need to go without causing permanent damage to my engine?

Answer
you might be able to obtain some coolant system sealer that might seal the leak if it is rather small, which it might be since the hearter core is obviously leaking.  You will know shortly after putting the sealer in if it has worked, if not all you can do is continue to add antifreeze till you get to where you are going, just do not let it overheat