2014 Summit 5.7 4wd 20" tires swapped to 18", added all skid plates
Just finished comparing 2 tanks of 87 to two tanks of 89. In trying to get a 0-60 comparison I got 7.x with the 87 and 6.6 with the 89. In terms of drivability, the 89 definitely seems to produce a smoother power flow. As best I could I watched the ignition advance thru the OBD port and there seems to be about a 5 degree retardation overall with the 87. Seat of pants is that with the 87 the engine is always bouncing the advance around as it senses pinging and you feel it in the power delivery. The power delivery just seems livelier, steadier, and more put together with the 89. Even the shifts seem smoother with the 89. With the 87 some shifts seem to cause the engine to retard making it feel like the shift itself isn't very smooth. There might have also been a 1 or 2 mpg increase with the 89 but that's pretty hard to judge.