*UPDATE* problem solved!! Coolant temp on hills GMC 3500

Thanks boys. Yes the temp drops like a rock when we crest the hills. I know I can add more cooling, but I need to know where the problem is coming from first so I make sure its gone for good. Has anybody noticed if towing without the tow/haul on can cause high temps? I saw on one forum where a guy was saying in tow/haul mode it fully engages the torque converter clutch in all gears but first to eliminate any heat being generated by the torque converter while towing. "I've never really used the tow/haul mode before.