I was out driving in the snow today and when a semi passed me it blew alot of snow over my truck. Just after it went passed my heater fan slowed down to about half speed. It did this whenever a semi or plow truck went past me. Also after this happened the first time I heard a squeal, almost like a belt, just before the fan started going full speed again. I checked the belts, but they all seemed ok. Anyone have any ideas what would do this.

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1997 F-150 Lariat
Ext Cab Short Box
4x4 Off Road Package
3.55 Gears
265/75 R16 Uniroyal Laredo M/Ts

My 2 cents worth

If you're gonna stroke it, POWERSTROKE IT!!!