When it's real cold my '84 4KQ will move 1-2" and the revs really
drop when I let the clutch out in neutral. This might be what you experienced.
It's due to the extreme thickening of the non-synthetic gear lube in the
trans. Perhaps someone even used something thicker than the "normal"
90W when refilling the trans. Switch to a synthetic gear lube and the
effect will be all but gone. I like the Mobil 1 90W and plan to install
it in the 84 "when I get around to it". I already run it all all the others.