Ambulance package seems like a PIA to me on a 6.0. It's already tight under the hood with heat management issues. The stocker is woefully underpowered. Stick something that is plug and play and at least puts out more amps at idle. Especially for bumping the two starting batteries back up after the glow plug draw-down. If you've got a big house battery, inverter, *****'n stereo, lights, winch, OBA, etc. then go even bigger to a 250 or 270A alternator.
The 270 XP produces 200 amps of charging current at 14.8 volts charge voltage at idle. Bam!
Is that necessary? Consider for a moment the poor FICM. At least it's not mounted on the engine like the trucks so not subject to the additional vibration but it's current sensitive. The OEM unit sucks. When cold and with glow plugs on the requirement is ~ 175 amps of load. The alternator can maybe provide 120A of that? The remaining current comes from the batteries drawing them down even further. Then, with the glow plugs off their not getting charged back up to a full charge. With a higher output alternator the ONLY time the batteries are being discharged is when cranking the engine. And that takes the load off the FICM. What many don't realize, it's not the underhood heat that kills the FICM, rather it's internal heat generated by the FICM itself as it compensates for low input voltage.