Just bought my AT4. Freakin dealer salesman admitted to putting in 87 octane to fill the first tank. Truck is stumbling. I get it and I'll be good by next week. Anyone have any experience using 89 Octane vs. 92 Octane? I only ask because I've read that the 6.2 can be used with 89. Sure it's possible, but I don't want to use 89 if it costs me performance and makes the 6.2 and 10 speed stumble.