I have an '04 5.3L ECSB. When I got the truck from my dealer, he said be sure not to use 93 Octane fuel because it would be a waste of money. He said in the newer models ( like the '04) 87 Octane will make your engine run just as good as if you put 93 in it. He also said 93 could wind up damaging it. If i need to pull anything, he said i could go up to 89 octane if i needed to. Is there any truth to this, or is this guy full of crap?