A few months ago, I purchased a 2016 "Certified Pre-Owned" Ford F150 XLT SuperCrew with 5.0 V8 FX4 (I think that is enough to identify it) truck with roughly 52,000 miles; it had been a lease return. So far, I have been VERY happy with it. I have one little concern though that I don't know what to make of at this point. It has now happened a grand total of three or four times, so not all that reproducible. If I were to make a guess, it seems to have happened when accelerating while going uphill. Each time, I'm going up on a winding grade, where I have to slow down for some turns then accelerate out. I have heard this high-pitched sound that sounds like a slipped clutch. It is because of this, I am thinking it might be an issue with the transmission or driveline. Does anyone else have an educated guess as to what may be wrong? As I've only put 5,000 miles on it, I'm hoping that whatever it is, it is covered by the "Certified Pre-Owned" warranty.