Please take a look at the linked threads in my post above yours to find more Outlaw Owners (we don't have a separate sub-Forum).
The Diesel was only available for a few years in the Damon era (Gen1).
For details see post #1 here: Class "A" Toyhaulers
The earlier Ford 6.8L V10 models were on a 22,000lb chassis, the Workhorse (8.1L V8/Allison trans) was 24,000lb and the Freightliner Front Engine Diesel was 27,000lb (5.9L from Cummins/Allison trans)
Owners of the Freightliner Outlaws do not see dramatically better power or mileage performance, but the GVWR is better. I blame this on not having the optimal gearing. But, it had airbag suspension and airbrakes...so obviously the selling prices of these units is measurably higher.
Reality is that each model chassis has its perks. Ford was, for years the most supple suspension and since 2011 is the only chassis used (since 2015 w/ 26,000lb GVWR). The Workhorse can provide the best MPG (mid to high 8's) and smooth operation with the big V8 and Allison 6 speed. The Freightliner FRED has Diesel functions (runs stronger but at lower speeds) and has a large capacity for aftermarket upgrades.