Mark, I think you answered your own question. Since this is the TMS wiki, I'll go out on huge limb here, and give you my opinion as a non-medicine practicing tennis player, that there's a fair to middling probability, that this could be TMS. I've never heard of "small fiber neuropathy", but it seems that the allopathic/medical/industrial complex is getting pretty good at coming up with novel structural dx's to cover for the fact that they don't have the solutions for the 80% of the issues that their patients are in the waiting rooms for that are TMS. "Small fiber neuropathy" sounds amazingly similar to the Good Doctor's Tension Myositis Theory of minute oxygen deprivation at the capillary level, excruciatingly painful but BENIGN!
Stretching your calfs to prevent injury prior to walking?--really! I could see a reason to stretch before doing a hundred yard olympic sprint but not for walking. Stress+pain+no traumatic structural injury=TMS. TMS is the volume control for the pain.
G'luck,
tt/lsmft