I put full tune on my 2014 2.5L about 2+ years ago after warranty expired at 86,000 miles, I bought malibu new off transport with 2-3 miles on it and now have 109,000k. Well worth price: much better throttle response, pulls stronger at all rpm ranges > there is a big difference. Normally run 87 top tier gas and have never heard any pre-ignition; tanks of premium top tier sometimes. They state to run several tanks of premium before you notice the performance gain, it does seem slightly better but not big difference. You will notice more torque in that it doesn't need to downshift as often going up a grade.
Tranny is also reprogramed as well. Upshifts now occur at much higher rpm with snappy upshifts until you ease up throttle. Downshifts are smooth sometimes and can get rough with hard downshift if caught when coasting and then depress throttle even slightly. Fluid was replaced x3 at 79,000k.
Some have reported a drop in mpg but mine actually increased by about 2 mpg. I drive easy all the time but do run through the max gears couple times a month to keep exhaust clean and try to avoid carbon buildup. Getting ready to change spark plugs soon. Before I retired my daily commute was 80 mile round trip 5x a week. My driving is 90% interstate and little to no city traffic. Car has been rock solid with not one mechanical issue, only repairs was 1 hub bearing, a/c compressor replaced, and radio head replaced > all under warranty.
You won't regret paying for the tune. All you need is a laptop and the cable adapter from trifecta.