A 5.7L hemi would be every bit as efficient as the 2.0t in the JLs and more efficient than the 3.6L. Since 2017 we've owned a 2017 ram rebel 5.7L hemi, a 2019 jlur 2.0t, a 2022 jlur with the xr package 3.6L, and a 2023 JT mojave 3.6L. The 2.0t was only slightly more efficient than the 5.7L stock for stock and the ram weighed about 1500lbs more. Adding armor, tires, and lift to the 2.0t and the efficiency dropped to 15-16mpg. The ram still got 17-18mpg after a lift and tires. The JLUR 3.6Lgets 13-14mpg as does the JTM. I would bet money that the JT would get better mileage from a 5.7L than the 2.0t as the efficiency of the 2.0 goes out the window when it's pushing boost constantly.
The R2.8 Cummins I think would be a bit small for the gladiator. I did the conversion to an 05 rubicon LJ and it’s a good upgrade for that size vehicle though.
“The R2.8 is built in the Cummins factory in Columbus, Indiana (500 engines in 2017) and only carries a 90-day warranty. They use engine blocks machined at Cummins's Chinese plant. The crate R2.8 engine meets EPA's Tier 0 (LDT 1 and 2) and Tier 1 emissions standards. In this case, it is suitable only for vehicles produced until 1999.”
Back in the ole timey days OTR trucks had gilder kits. A glider kit was a chassis and cab, the guy or company that bought the truck would slide in what they wanted. N14 Cummins, 3406 Cat, Series 60 Detroit, any combination of 9,10,13,15,18 speed Eaton trans. Personally if they just sold a chassis without a powertrain would be nice. If you want a 3.6 or the Italian thing fine, if not then a blank page for a 5.7, 6.4, or an LS engine with out paying for the engine and trans. Frankly there are much better mills then anything they offer now or in the future.
I would personally like just a 5.3 LS in one. That would wake up this truck so much. I also think the oldie but goodie 4.7 HO would be super nice. My Jeeping buddy and I were looking at options last weekend as I just happen to have a low mileage 4.7 HO from the WJ days laying around. We crawled all over mine looking at what we needed to repower it and leave NOTHING OEM behind. Strip it down to body only, even the dash goes away.
I hate 4 bangers in a truck. I hate 4 bangers with a turbo. All they do is wear the 4 banger out faster. Look at the 2024 Taco,They get worse milage than the 6 cyl. That's why I didn't get the Taco.
seems like a loaded question honestly ... doesn't matter if it's more efficient, or more torque ... if it doesn't last as long. Assuming an engine with enough torque/horsepower, the big question comes down to total cost of ownership ( for a daily driver ).