New owner. Not sure if the idle behaviour is normal.

Just got an 06 f250 6.0 diesel, first
diesel I've owned. When I sit idling it
revs up like it normally would when
you first start it till it's warm enough. I
think it's normal anyways. Then it
idles down when it's warmed up. But
if I drive it for a bit and stop and park
or continue to stay put and let it
continue to idle it idles up to
1000rpm give or take then back
down to 900rpm after about 6
seconds it does this intermittently
about every 2-3 minutes. I live in
Alberta and it's winter right now so
it's cold but I don't think after two or
three minutes at a lower idle it would
cool off enough that it needs to rev
up to get a higher engine temp. If
that's the case it should stay at a
1000rpm steady idle instead of up
and down. Water temp is normal but
the tranny temp does look a little hi
for just sittin here. Is this normal or
could I have an issue electronically or
something in the cooling system
since the transmission temp seems
high to me for idling? Not sure the
tranny temp all the time while driving.
It just occurred to me now that it
could be a factor. And my heater fan
seems to speed up and slow down
when I drive too