Hi,
I don't have any specific experience of diabetic neuropathy but I am under investigation by the rheumatology team due to years of joint clicking and pain and muscle loss. At times I have numbness down my arms and in my hands but it is very short lived. Like you, I also have relatively low hba1c levels. Have you been referred there and have they done any bloods to rule out lupus etc? I know you said you had lots of tests done.
Sorry I don't have any real advice to give. I hope they find out what's going on and can help.
Neo88