I bought the truck from a dealership a few weeks ago. I'm pretty sure an elderly gentleman owned it before me and it was a one owner vehicle. Anyway, it says on the gas cap that E-85 or premium fuel is recommended and it is a Flex Fuel vehicle. I've seen people on forums destroy those who run anything less than 91 octane fuel in 6.2, so I decided I'd try 93 and see the difference. (Assuming the gas from the dealership was 87) Recently, I pulled up to talk to a buddy and he pointed out a ticking/clicking sound. He asked me if I was giving it hell and honestly maybe I was. Later on, I floored it to pass a school bus and just test out the power, but once I got up to 80 mph, instead of still climbing, it started slowing down. I was holding the pedal to the floor, but the truck was not accelerating anymore. I let off once it reached about 55 mph and it seemed to be fine after that. The check engine light came on immediately. My first thought was a clogged cat. I'm not sure if the 93 octane gas, the ticking, and the loss of acceleration are related, but from the information I have gathered, one of the cylinders is randomly misfiring, (possibly due to high octane?), and that may have been what cause the clogged cat? Maybe I melted the cat by flooring it with 93 in it and the sound I hear is the air trying to escape. The next day, the check engine light was still on, but I noticed almost a hissing sound when accelerating, but I don't think it'* hissing like a vacuum leak or anything like that. It sound like it'* under the cab, so I guess it'* either the cat or the trans. Then, it did it again when I floored it, trying to see if it would happen again. Since then, the check engine light cut off and I haven't foored it anymore, but it'* still acting a little strange, hissing during acceleration, and ticking/clicking at idle. Mainly after the engine slows down a little after start-up. Am I just over paranoid?