"Godzilla" Ford V 8

I'd be interested to know how many HP the pickup truck version produces at 3750 RPM. My guess is that it's not much (if any) more than the motorhome version.

^ What he said. Although it doesn't really make sense since all the F series up through the F450 get the full power version and the gcvwr of the E series is much lower than many available F series class 3 and 4 trucks.
Similarly, the E series, cutaways, Class A chassis and bread trucks also only come with a 6 speed.

Moreso, I would bet it comes down much less to the durability and duty cycle rating and is primarily a cost saving measure. Which is somewhat easily justified in that the "performance" (power and speed) of a utility vehicle is much less of a selling point to plumbers and RVers than it is to F series buyers, who actually tow much heavier with class 3-4 trucks.
And with no real competition to beat (other than Chevy who isn't even close in market share and also not winning the power/transmission battle anyway), no reason for extra cost to give someone a faster class C or work van.

In other words, Ford is not chasing a carrot with these models. They are the carrot, albeit a lower HP de-rated carrot.

Engines are normally de-rated for ‘severe service’ applications like an RV where there is no such thing as “empty miles” like the majority of driving is with a pickup truck or even a cube van. It makes a big difference in durability and longevity.

In Ford’s case, it was something they’ve been doing from their earliest days with their farm tractors.

As an example, a ‘typical’ Ford tractor, a 3000 utility tractor has a 2.6 liter (158 cu. in.) gas engine, de rated to 46.7 hp. By comparison, a pretty well-reputed typical automotive engine, the Mitsubishi 2.6, is rated at 135 hp.

We have a Ford 3000 gas tractor, the engine has had (or needed) anything but maintenance since it was produced in 1965, it currently has a little over 10,000 hours on it. If you use the conversion speed of an average of 45 mph, that would suggest it has the equivalent of 450,000 miles on it. It still has no real wear evident, no oil consumption or blow by, etc.

I guess the idea was for the rv engine to get better mpg's.....???
bc it's operating at lower rpms where its tuned to get peak HP and torque at a lower rpm ,
where the fuel injection settings are tuned at peak.

Super Duty chassis with the 7.3 engine is tuned to produce 430 hp at 5,500 rpm. The Premium RV 7.3 is tuned to produce 350 hp at 3,750 rpm.
I think its better suited for the rv which is always hauling its weight where a P/u is not. To have power early on , lower rpm's, is a benefit in an rv.

I would guess it's de-rated because of the heavier duty application. Also, cooling may be an issue with the tighter confines of a van engine compartment versus a truck engine compartment.