ktbr writes:

You don't say what the air temp is.

It was -1° C at 5000 feet.

But anyway, this is all
academic in terms of a simulator, but there any number of
things that can affect the airplanes actual (TRUE) airspeed:

Weight
CG (loading)
air density (temp/pressure)
power (RPM)
propeller efficiency
how slick is the fuselage/wings? (parasitic drag?)

Through various combinations of these an airplanes max
true airspeed can vary considerably from ;book/ values.

I've been thinking and two possibilities come to mind: cowl flaps
closed, and prop speed reduced. I didn't think that cowl flaps made
much difference on a Baron, certainly not 20-30 kts, but maybe. I
also thought that reducing the prop speed might have something to do
with it. The aircraft slows down initially when I reduce the prop
speed, but up to now I haven't watched it over time to see if it ends
up moving faster, so I might try that.

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