I have a set of 5 mountains I'm riding in preparation for a 50K ride in a few weeks. What has worked for me was just the opposite. Instead of racing to the hill at 12-15mph I now cruise to the hill at 7-10pmh and when I get to the hill I go down to 5-6mph. I actually get over the hills faster because I don't have to get off and rest like I did in the past. Plus I found my legs are getting stronger with every attempt at the hills. Not sure if it will work for you, but it has worked so far.