In most cases, higher octane probably won't help & may even do a bit worse. One exception- if the car is getting a little motor oil into the combustion chamber, whether from worn/stuck rings or worn valve guides, more octane may help, because motor oil degrades octane.
BUT: The last tank I ran through the Dakota had 8 gal of 93 in a 22 gal tank. Since I bought the truck 6 weeks ago, best milage has been just under 16 mpg in my current mostly short hop driving. One tank was under 15! So: I reasoned that with the Dakotas 3.9 V6, too-high top OD gear(0.69, w/3.55 rear axle), and 30.3" tall new tires, it was struggling to maintain that high gear without downshifting. Really- it would be hard to come up with a better set of conditions to cause it to always pull timing- and pulling timing is death to gas mileage! It would downshift for just about anything if you were under ~62 mph. Looks like I was right- At fillup after the 1/3 Super, with FP, mileage had gone to 17.578 mpg. Nice difference, huh? And not too bad for a near 4000 lb vehicle that rarely goes more than 6-7 miles at a hop these days. It also climbs a pretty steep hill at only ~50-52 mph(50= ~min speed to shift into OD) without downshifting. Current fill is also a bit over 1/3 Super(station claims no Ethanol in any of their gas), will pay very close attention to this tank's mileage too.
This makes me think that 1. Sometimes a little extra octane really *can* help! and 2. My truck has not received the dealership Mopar "Death Flash" to the computer. If it had I doubt extra octane would help at all.
Please note that I tried this for a specific problem that seemed to cry out for a little more timing, hence a little extra octane. As always, YMMV.
