Users of the big gassers: Dodge 6.4, GM 6.0, Ford 6.4....... Can the lower octane be used or do you need the higher octanes????? Colorado we have either 85, 87, or I think 91..
If you drive on steep grades, putting higher octane will make the engine working better. Modern engines have anti-ping sensors, so they will adjust for lower octane if you use it, but lowering the performance will make for gear downshifting and in the result - higher fuel consumption.