On my 05 f-350 Im having concerns on a voltage readout problem. At KOEO I get a reading of 48.3 volts. After I start engine it drops to 33.3 volt and takes around 8 mins. to get back to 48.3 volts When I rev it to 3000 rpms within that 8 mins. I notice a miss, but when its hitting 48 volts it smooth as can be. I checked plug ins and wiring. Is my FICM on its way out or do I have another problem.