Having owned a Cummins diesel for several years and supporting the extra costs and servicing requirements, here's my take between the Hemi and VM Motori:
The horsepower is much less on the diesel but the torque is slightly higher--+30 foot pounds. However, torque in the diesel, like most diesels come on early so you can start moving the load sooner without having to run the engine to near max. Is there enough difference in torque to justify the diesel for towing? I don't think the Grand was designed for any significant towing compared to a regular truck. IF you are going to tow regularly at or near it's limit, 7,000 pounds, you owuld be better served with a pick up truck--prefereably a deisl truck that generates 650-800 pounds of torque and all the proper gearing, coolihg, sway control, etc. Not only is it just weight, but wind resistence, bumper weight, weight of the passengers and gear, water, fuel, fluids that accompanying a large camper or boat or ATVs. Occassional towing of a jet ski or ATV can be handled by the Hemi just fine---it's the same used in Ram's 1/2 ton and 3/4 ton Power Wagon--though the Power Wagon uses a 4.56 rear ring ratio to make up for a smaller engine compared to the Cummins.
Diesel used to cost 20cents less than regular gas. It now runs about 15-25 cents higher than premium because what used to be low sulfure crude (50 ppm)is now requried by the EPA to be ultra lower sulfur crude (15 ppm). The price per gallon is now quite high to the extra processing using some sort of hydogen to remove the sulfer.
Diesel's next benefit used to be better fuel mileage. Will we actually be getting 25-30 estimated or will it be closer to 20-25 mpg actual? Given the exta 15-25 cents per gallon cost, this increase in mileage would be washed out by the extra cost in fuel.
Diesel engines are supposed to last forever---will you keep the grand for 300,000 miles? Of course, industrial grade diesels like the Ram Cummins 6.7 is rated for 350,000 miles before an anticipated rebuilt---and that includes all the Cummins 6.7 used in commercial hauling uses. Personal use Ram Cummins often lasts 500,000-750,000 without even open the head. Will VM Motori be as stout?
Diesels are now chocked with EPA emissions such as engine gas regeneration (EGR) where exhaust is piped back into the intake as neutral inert gas to reduce exhaust gas temperature---sort of like breathing in your own farts, particulate filters and using raw diesel fuel sparyed into the particulate filters to burn off soot, and using DEF (Dieself Exhaust fluid--eseentially pee water) to convert exhaust gases to less toxic emissions. The Grand Cherokee Diesel uses an 8 gallon tank to hold DEF. In cold weather, the DEF tank uses a heater to prevent freezing. However, reports from the GMC/Chevy truck forums have complained of DEF freezing and cauisng the engine to go into limp mode. There are frequent complaints on the truck forums about DEF tank sensors sending "NEAR EMPTY" when it is half full--again causing the engine to go into limp mode. Very inconvenient when you are out in the middle of nowhere to go into limp mode. Should you carry an extra 5 gallons of DEF just in case? No problem in a pick up, but the Grand is not a pick up and space is at a premium.
Will there be a requiremnt to clean the EGR every 50,000 or so miles? It costs about a thousand bucks to clean out the EGR and replace both filters in the CCV filters and valves in the Cummins as it requries pulling the EGR out and soaking it out. Just another expense to plan for.
Will you need special CJ-4 API rated diesel engine oil? We use 5w-20, but any old 5w-20 will do. Diesels have been forced to use CJ-4 if not CK-4--the next generation oil, to cope with soot build up and EGR and particulate filter and emissions. Using other than CJ-4 can harm the emissions and engine components. Another cost and service consideration. ANd changing fuel filters in diesels is VERY IMPORTANT. Every 15,000 miles. How much for the Grand Cherokee diesel?
Becuase Cummins will last until the next ice age, resale value--the next diesel benefit, is high. Will VM Motori be anywhere near as good in resale? Even with all costs, the resale justifies the $7,500 extra for a Cummins, or the $4,500 for the VM Motori. Will the resale hold to recoup the cost?
I think these are all factors to consider before jumping on the small diesel bandwagon with eyes glazed on the 25-30 mpg promise.