I have a new 2007 GMC classic 2500 HD with 1500 miles. While towing my 10,000# camper in the mountains the temperature climbs to 235 degrees before the fan clutch locks up. The temp. then drops to about 205 degrees and stays there. The temp climb to 235 only last about 1 minute is this normal or do I have a cooling system/fan problem. Thanks, Paul.