Could borderline diabetes cause nerve pain in my upper back?

Mononeuropathy: Possibly but unlikely. Neuropathy particularly affecting isolated nerves usually is associated with more severe long standing diabetes and may not be all that painful.

Maybe: Type 2 diabetes develops gradually, and some nerve damage may occur before a person is diagnosed with actual diabetes. So a person could have pre-diabetes (preferred term instead of borderline diabetes) and have neuropathy. However, neuropathy most often causes problems in the feet first, so pain in the upper back may be due to something else. Ask your doctor to check it out.