6.0L FICM Issue?????????????

Okay my 2005 6.0 Powerstoke is having issue with onlu 60K on it!!!

I was having cold start issues and rough idle that was getting worse so I assumed after lots of reading it was the FICM. So I check it out and the voltage was low around 37 V both with the injectors buzzing and while running.

So I decided to try and repair re-soldering the power side circuit board as I have read so many people do with great results. I followed the process and put back in and got great voltage numbers, 46.4 injectors buzzing, 47.8 while running so I was ecstatic. The drove all day and it ran like new. The next day it fired right up but I had rough idle and it stumbled when I stepped on the gas again. I re-checked the FICM and the voltage was back to 32 Volts basically.

I had the batteries load tested and the 5 year old passenger was bad. It did crank a little slow so this wasn't a surprise. I bit the bullet and bought 2 new Motor Craft 850 CCA and replaced both batteries.

I removed the FICM and re-soldered it again. This time I got 46.4 at injectors buzzing and 47.1 while running. Again it ran great for a while then later today its back to no power and stumbles when you step on the gas but it does start pretty easy.

I'm sure if I check the FICM the voltage will be low again .

While running the batteries are at about 14 volts so I assume the alternator is doing its job.

Not sure where to go from here. I'm afraid the buy a half shell FICM or whole brand new one because I'm not sure whats failing it. The only code I get is the low injector circuit that I'm sure comes back after the FICM falls to low voltage.

I don't just want to start spending thousands on this dang thing as you can easily do with out knowing whats wrong.

Any help is greatly appreciated.

Jerry