@davidpn When you describe this, and that the doc doesn't think it is your neuropathy, I just have to ask whether you take a beta blocker (such as metoprolol) for your blood pressure?
For reasons that don't seem to be completely understood, these can cause a sensation of "heavy legs" while walking in some people. Other medications that have a tendency to make legs feel sluggish can include diuretics and statins.

Sometimes side effects of medications can masquerade as part of a disease or condition we have...often alternatives can be found that help improve our quality of life. It might be worth a chat with a PharmD - a doctor of pharmacy trained to evaluate the overall effects and interactions of all the medications you use.

Sue