I would say it is not 3rd specifically that they are after but a given road speed due to friction/heat build up at higher road speed which may not be present so much on coast down.

A rally car may top out at 60 in 3rd where as a big engined road car may be doing over a ton so to just say 3rd is pointless.

Because i was told so is not really an answer i would want my RR operator to give. I would want them to know WHY.