I am running 87 octane in my '11 RG but I add my own octane booster, 4 gal of 87 unleaded with 1 gallon of 110 leaded racing fuel. My mileage is nearly 5 mpg better vs running the supreme 91-93 octane, 44mpg vs 39.2mpg. The price is a little more expensive, but no pinging, and the performance is even noticeably better. I was 2-1 regular vs racing, and now at 4-1 and that is where I will stay. After a couple of months I will run the numbers and refigure the averages...
Of course, this is of little help to the OP... I hope it is starting to loosen up a bit!!!!!!
103" w/Race Kit,Stage IV 117HP 111TQ
SE 259E Cams
SE Heavy Breather AC (Scott's modified)
SE Race Tuner
V&H Power Duals & Hi Outputs
SE CNC Heads 10.62/1 w/SE 58mm TB
John Scott port matching
Renegade Racine wheels. 21x3.5/ 17x6.25