Zenrunner, I wonder if a run/walk method might help you at present. Jeff Galloway presents it in a helpful, systematic way, particularly in his book "Running til you're 100". As an old runner I find it is specially helpful, as by changing the run/walk ratio even in mid-run one can make any outing harder or much much easier at will. It is gentle on the body, only the ego suffers when not doing "joined up running". But a zen runner should be able to cope with that! Good luck.