I got left achilles pain when I first started (road) running 2 years ago when I ran over 6 miles. I went to up and running and had a gait analysis and was diagnosed with the same as you - right foot OK, left pronating. I bought some New Balance support trainers which stopped the problem immediately. Started fell running last year, wearing Roclite 295s which have been great. I think you only need support shoes with pronation correction on the road, due to the constant pounding in the same position.