2021 Silverado 6.2 High Country

[glockman49]

I bought the unlocker kit and i-3 for my truck. I loaded the 87 tune for better fuel mileage and more torque in. I took a 80 mile road trip soon after and found I dropped about 3 mpg on my 6.2. When I had the old tuner installed on my 2018 Yukon with the 6.2, I was able to increase my gas mileage by about 3 on the highway. This time with the same load, I lost gas mileage. Any idea why?

[06MonteSS]

With that 6.2, you need to use at least 91 octane gas, so make sure you are using GOOD 91/93 octane gas, it makes a difference... mobil, exxon, sunoco, amoco, bp, chevron are best brands to use, with mobil and exxon being the best... Even the factory stock tune timing/spark advance settings are meant for at least 91 octane...  

NEVER use Shell, walmart/sams club/bj's, mom-n-pop, or no-name brands, as it's crap gas/additives that tends to cause a lot of knock retard and less performance/mpg...

[glockman49]

Evening Lew. I'm running 91 Octane. I just couldn't see why I lost so much on the gas mileage end running all interstate. The engine is running stronger but I was after some fuel economy as the 6.2 has plenty of power for me. I'm going to pull the load out and retest and see if I get my prior average back.

[mikel]

did you adjust the tire size when you installed the tune?