shin splints are notorious for forefoot strikers. it happens when the calf muscles fatigue and fail to support the foot properly. midfoot striking is the right way to run. hmmm.... overpronation would lead to foot pain. that's when your foot turns inward when you run. underpronation is when the foot turns outward when you run, and would still result in foot pain. same with high or flat arches not getting enough support. the shin splints are a secondary factor to those, so if your not getting foot pain first, then i doubt it's any of those issues.

do you lean forward when you run? the spine should be straight ideally. this would lead to shoulder pain more than it would anything else though.

I think... lose the insoles! it's gotta be that. do you wear special insoles when you walk and run?