if you are only considering the v6 and the diesel, you shouldn't be even considering the price of fuel. saving money on fuel is only a big deal if you're considering the HEMI. as you stated, it will pay for itself quickly. the average MPG ratings for 4x4s (who buys a 4x2 jeep anyway?) are 24.5 for the diesel, 20.5 for the pentastar, and 17 for the HEMI. the diesel will pay for itself in a couple years since it's $3831 over the HEMI (really only $1161 if you don't consider the luxury package as part of the upgrade price). if you're buying the pentastar, it's going to take a long time to recoup the cost, but it will eventually. i think the estimate i calculated for my driving scenario would be somewhere around 8 years. this doesn't make the engine free after 8 years, it just makes total ownership cost the same. but since you have to jump to the limited to get either engine option, it could potentially be a much longer time in your situation. saving money on gas isn't the best reason to buy the diesel though. you should buy it because you're going to enjoy driving it. The engine simply drives differently than the gas, and you should drive them back to back to see if it's for you. i recommend going into sport mode as soon as you start the car (just pull the shifter back one more time after D). pros include:
1) MUCH more power if you're going to tow or pack a family with camping gear. the pentastar will lag fully loaded, the diesel won't even notice a 5000 lb load.
2) engine longevity. if you're going to keep the car for a while, the diesel doesn't have to work at all. RPMs are super low at 80mph. this benefits off road too, all the torque is at 1800 RPM.
3) low end torque is amazing, espically at low speeds. punch it and it goes. punch the v6 and it will downshift,rev way up, then you will feel something. find a big hill on a test drive, and floor it on the way up, it will be tough not to smile.
getting to the point i paid 7% below invoice with the DC group buy. 48880 MSRP went to about 43500 for my diesel. you could get a diesel for less, i added the off road package which was $2221. you pretty much have to include nav though at only $356. i drove 430 miles each way to go pick it up all in one day. i left at 0445 and was home by 2200. i'd to it again in a heartbeat.
you should only be looking at invoice prices and then go down from there. they can be seen here:
2014 Grand Cherokee - Ordering Information and Pricing