Why does my 4.6L engine sound like it is reving high, but it's not? Starting from a stand still, it sounds like high revs, but never gets of 1500 RPM.

 

My first thought is that your fan clutch may be the source of the sound. I had a similar experience around 250K, replaced the fan clutch and solved it. If it helps, I think I recall the sound was much more pronounced on hot days.
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Rick

 

I purchased a new fan blade about a year ago. Noticed the sound started a few months ago. Just because it is new, doesn't make it good. I'm pretty sure you are right.