[2000mudder]

you and the dealer are both correct. you shouldn't have to run higher octane than the manufacture calls for but at that altitude you might have to run 89 octane gas. what kind of gas are you using? is it straight or blended with ethonol? aks the station what kinda gas it is and try switching to the other kind. the ethonol blends start with a 84 octane and the 10% ethonol brings it up to 87 octane. straight 87 octane gas might work better for your motor.