Weird fan activity

Reading the post about a Ram's high idle reminded me of one of my Dak's little foibles (2001 Dakota, 4x4, 4.7l v8):
When the weather is cooler - I used to think "when it's in the 60s" but
that doesn't happen here - when I first start the truck and drive off, when I shift from first to second, it sounds like the engine fan revs high, holds at that speed a few seconds, then drops off to normal(used to think it was the engine). Same thing, sometimes, second to third. Soon as the truck warms up a bit, this stops.
Doesn't seem to do this in really cold weather, or warmer weather, just in this middle weather where it's cool, but not cold, in the morning.
Is this normal? I'd say it's not a problem, since it's been going on for nearly 6 years now. Just curious as to why this is happening.
jmc
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snipped-for-privacy@NOjodiBODY.HOMEus says...

I have the exact same issue with my 97 Dakota, 4x2, 318 V8. It's been happening since it was new so I guess it's not a problem. Just kind of annoying.
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