My 2001 Chevy Sub. tends to run hot whle the engine is under a load. 3 years ago, I pulled my camper 14 hours without any problems. Last year I took a 70 mile trip and the engine ran approx. 240-245 degrees on the ride home. I had the thermostat and waterpump changed. It ran hot again this spring on the same trip. I changed the trans. cooler and the fan clutch. I have the orange antifreeze and have flushed the system 3 times in the last 2 months. I passed an 18-wheeler going uphill the other day (without a trailer) and the temp got up to 245 degrees. My mechanic used a bore scope to look into the radiator and didn't see any trash or other notable problems. My sub. has 139,000 and my camper weighs 7800lbs., and I don't know which way to turn at this point. Any suggestions?