I have the same truck (7 years now and still loving it) and what you've described isn't unusual. These trucks aren't made to cruise at 75 mph, uphill, fully loaded. They can do it, but they're not designed with that as the center of their "comfort zone". They're engineered to provide optimum performance for 60-65 mph, one or two passengers, and not much cargo - which is where 98% of total miles will be logged for most owners. I don't find what you've described as unusual.
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