This review study published in 2008 compiled data from two published clinical trials involving 1,679 subjects receiving 2g daily assessing for pain scores in patients with diabetic peripheral neuropathy. Both studies found improvements in pain and one also found nerve conduction.
Evans, J. D., Jacobs, T. F., & Evans, E. W. (2008). Role of acetyl-L-carnitine in the treatment of diabetic peripheral neuropathy. The Annals of pharmacotherapy, 42(11), 1686–1691. https://doi.org/10.1345/aph.1L201