Life expectancy of 3.5

[FordTechOne]

My only point is that when adding more parts that you depend on that have a non-zero failure rate, your reliability will always go down. It's just math.

This is generally true; if it is assumed (for arguments sake) that all parts have the same probability of failure, adding more parts means a higher probability of an issue occurring. There are real-works exceptions to this of course, for example a fuel injection system has many more components than a carburetor, but provides much improved reliability.

I have never owned a car/truck in my entire life that was left naturally aspirated or that didn't come with some sort of forced induction. I turbocharged my first vehicle (A Jeep wrangler TJ 4.0L) and did a lot of prototyping various turbos and data logging on it trying to make it better and better.

I have heard those 4.0’s put out some serious torque with a turbocharger. Similarly to when people were installing old GM 6.5 Diesel turbos on Ford 4.9’s; not a huge power increase, but they could put down over 500 lb/ft at the wheels.

Why do you think none of these trucks feature a turbo gasoline engine? Why not just design a turbo gasoline engine for the 3/4 ton and 1 ton trucks? I know you have a lot of experience and knowledge about these trucks so I'm genuinely interested in what you think.

From my experience, the reason is duty cycle. The advantages of downsizing and turbocharging engines is that they are more efficient than a larger engine of the same power output under all conditions, with the exception being maximum load/wide open throttle, at which point both engines consume approximately the same amount of fuel.

In HD applications, the vehicles are often heavily loaded or used for heavy towing, with many at maximum GVWR or GCWR. In these applications, the engine is operated at full throttle/load, in other words high duty cycle. In this case the smaller turbocharged engine wouldn’t provide an efficiency benefit due to the duty cycle. Therefore, from a thermal management and cost perspective, it makes more sense to go with the large N/A V8. In fact Ford arrived at 7.3 liters not to pay some sort of tribute to the old diesel, but because they found that it offered to ideal balance of power and torque (both peak and across the curve) as well as fuel efficiency when heavily loaded.

Here is a good article about the engine from Popular Mechanics:
https://www.popularmechanics.com/cars/trucks/a27310861/ford-73-liter-gas-v8-engine/

EDIT: I also wanted to mention that Ford has done a lot to make the engine more reliable than other manufacturers. For example, the cylinder head temperature sensor. There is a table in the ECU to retard timing with increased temperature. Most cars have to rely on coolant temperature for this table but having one in the head gives you far better readings with drastically reduced reaction times. The end result is reduced chances of engine knock compared to a legacy coolant temp sensor.

All good points. Another reason CHT was added was to prevent an engine overheat condition that can occur when coolant is lost and the ECT is exposed to air. The ECT will not read accurately since it is no longer submerged in coolant, so the PCM will not know to enter the failsafe strategy that limits power and shuts down cylinders.