This one actually showed airspeed (as well as ground speed and "true air speed"), but the big clue we had slowed was the reduced noise from the engines and the sudden feeling of deacceleration followed a couple of minutes later by the reverse happening. I don't think it was wind.
ETA: I hope this link works:
https://flightaware.com/live/flight/.../KDFW/tracklog
At 10:31:25 pm EST you can see the speed drop and then recover shortly afterwards.