Yeah QT is great and their gas is as cheap if not cheaper than Costco. Also their 89 is rated lower than it is. It's about 91-92 octane. I forget you guys only get 91. Bah. California and their craziness. Lol
If the resulting problems happen at Costco then it's just smart to avoid. Maybe a bad batch or just the additives aren't playing nice with your injectors. If happens again and you have stayed away then process of elimination begins
I hope that the issue is resolved though. Warranty or not it can be a hassle.