dont try and rid of yourself of all your mass up top. dont know what workout you do but i would start doing more low weight high rep stuff. swimming as you mentioned you may do would be a great option.

as for hill repeats, they make you an animal over time. i started doing them earlier in this year and it helped me get over a hump ive been on for some time now. i stopped doing any upper body, which i know isnt good, and now look like a skeleton. with upside down pears for legs!!!