Like you, I have been putting in a good pile of miles for several years. I have already been doing intervals. But I was stuck at 13 - 14 MPHs average.

In February I started doing some work with weights, leg extensions, hamstring pulls and lots of squats. I use dumbbells for the squats. I am consistently posting average ride times in the 15's and am climbing better than ever. This is what has worked for me.

I also am put a scoop of BCAAs in my camelback and have a protein smoothie at the end of every ride. The smoothie keeps me from loosing the extra 10 pounds that I need to shed, but I am stronger.