My old QH, Twister, almost ALWAYS bucked going up hills. It was never a "something hurts" buck, nor was it a actually trying-to-throw-me buck, it was purely high spirits on his part. His previous owner before me had always galloped him hard up every hill when he rode, so it became a habit for Twister to really cut loose whenever he saw a hill. It took a lot of walking up all hills
for a long time to get him to approach a hill calmly without jigging, side passing all over the place, and puffing. He still almost always threw in the occasional buck when we did canter on hills, I just always had to be prepared for it - if I wanted to canter on a hill, he was going to get a little too happy about it.