OB2 code P0460 Ford 2003 F-150 SC 2 WD 4.6 L X

Question

I have replaced orig. alternator at 11500m and approx. 1 month later Im getting a PO460 code. I have replaced fuel pump and fuel sending unit. And still getting code . Inside cab fuses ok. And instrument panel still tweaking out (fuel gauge) speratic when driving,(voltage gauge)drops to lower end. E-Brake Light comes on/off.
How should I start with diagnostics ? Oh and my front disc pads are worn and need replacing, if that might have anything to do with it ? ( I dont know ).
Thanks