One oil change in 11000 miles?

My new 2017 F-150 recommends oil changes every 10,000 miles or 1 year. The first oil change at 6,000 miles with a second at 11,000 miles wouldn't worry me at all.

my mb says every 10k I change at 8k that rv is safe in my eyes.

You could go the lab route, but how does the oil look? Milky at all? First concern would be if there had been any moisture buildup due to long term storage. Did they excercise the engine at all? What types of trips did they make? If they took the unit 20 miles to a local lake a dozen or more times a year, I would think it was fine, all the fluids were warmed up and circulated frequently. Or was it one or two 3000 mile trips in all those years, meaning those fluids sat dormant for long spells.
And that same concern would go for the tranny too.

If it already had an oil change at 6K miles and the moho now has 11K miles, it tells me it's due for another change right now. I won't be too concerned.

With today's kinds of HI-Tec oils I wouldn't think it would be a problem. Do you know the kind of oil the owner was using?

Take an oil sample and have it completely analyzed. They should be able to give you a handle on how much acid and other contaminates are present. Be sure to tell them the situation you are in and ask for their recommendations based on what they find. Blackstone Lab or JG Lubricant Services are a couple of good ones.

6000 miles is not that bad , your heading says 11000, that is 2 many