i'm at 45k in my 2000 ses. I took a drive up the coast about 200 miles one weekend at 80-90mph straight up. For some reason I decided to fill 'er up with 91 before the drive and I could almost swear that since then(about 3 weeks ago)my car is driving WAY smoother. Is it the gas or the fact that I got to give the car something other than the normal stop and go and that helped? I tried 91 again though with regular driving and it still feels better. smoother shifting and faster acceleration.