I have a 2001 Silverado with a 4.8 . I have done the electric fan swap have the nelson performance harness and an 130 amp alternator. This setup has been work ok. But recently I have had an erratic voltage gauge bounces from just above 14 to about 12 even with the a/c off, with the a/c on it drops and stays. Checked all my grounds and battery connections all is well. Any ideas?