Does the 3.0 have variable valve timing? Mine is in the shop and they are saying the cam phasers are bad but I can't find any reference to the diesel even having cam phasers.
Like most diesels on the market today, the 3.0 PS does not have variable valve timing (neither does the 6.7 for that matter). I will try and simplify the reason as follows: VVT was created to help gasoline engines provide more power and better fuel economy.
For a gasoline engine to be efficient, the goal would be for the engine to operate at a stoichiometric air-fuel ratio of ~14.7:1. This allows the fuel in the combustion chamber to completely burn. However, to produce more power, we need more fuel; more fuel requires more air. As the gasoline engines RPM increases, volumetric efficiency decreases due to losses from the throttle valve (gasoline engine speed is controlled by the amount of air inducted, sometimes referred to as pumping losses) and high RPM (time that the inducted amount of air has to enter the combustion chamber). To combat these 2 losses, VVT was created to vary the duration the valves remain open and closed to increase the volumetric efficiency over the RPM band of the engine to keep it operating as close to the stoichiometric air-fuel ratio as possible under differing load demands.
Conversely, a Diesel engine does not have a throttle valve (engine RPM is controlled by the amount of fuel that is injected into the combustion chamber). Additionally, a diesel engine produces much more power at a lower RPM range and typically has a much lower maximum RPM. This drastically increases the volumetric efficiency of a Diesel engine (no pumping losses due to a throttle valve and maximum power production and lower RPM). Efficiency is also increased in modern diesels by operating with forced air induction. This makes Diesel engines run much more lean than their gasoline counter parts (meaning the engine has more oxygen in the combustion chamber than is required for a complete burn) essentially making VVT a complexity on the engine that will produce very little benefit. And this is why the Diesel engine is considered to be more efficient than the gasoline engine.
This is not an exhaustive explanation, I tired to hit the high points and keep it fairly easy to understand. The mechanic was probably mistaken (as the 3.5EB has had rattling problems with the cam phasers) but the 3.0 PS does not have cam phasers (the cams are belt direct drive).
Hope this helps answer your question.