AAA stated that the cost of premium was 20%-25% more. Here is Calif, reg is $2.99 and Premium is $3.19, a $0.20 difference. $0.20/$2.99 * 100% = 6.7% cost upper, so for a 5% increase in MPG, it's difference lost in the noise! I will buy premium.
California here also, this morning when I filled up at VP regular was $3.499 and premium was $3.759, a $0.26 difference. 7.4% cost increase for premium.
When my 2018 was relatively new (but broken in, I think I did the test starting at about 8000 miles) I did a test for about 8000 miles. I had been running premium from new, as that is what was recommended. Then I switched to regular for ~4000 miles of my "normal" driving, and compared it to the next ~4000 miles with premium under as close to the same conditions as I realistically could do on the street. Almost every tank of fuel was from the same station. During that time I averaged 15.4 MPG on regular, and 16.7 MPG on premium. This means it looks like I did about 1.3 MPG better on premium than on regular. Or about 8.4% better. If these numbers hold true then premium is a no brainer for me, I save money running it.
However, I also feel like the truck ran stouter on premium. There was nothing wrong with the truck on regular, it ran great. But I think, I feel, like it just ran better on premium. Yeah, sure, I could easily be talking myself into that opinion. I have owned other vehicles were there was a clearly detectable improvement on premium. But it did honestly feel better on premium.
Regardless, the truck seems to (total opinion) run better, and in my admittedly meager testing it was cost efficient to run on premium. So premium it is.
But even if the testing had not seemed to indicate premium yielded better mileage, I quite possibly would run premium anyway. If the mileage was the same for regular and premium the cost increase for my average driving year would be ~$250. Premium would cost me about $5 a week for something that I feel makes the vehicle run better.
T!