I have found that the 707 will rock gently if I slow down too much on approach too. I use it as a way of figuring out the Airspeed versus Weight versus Maximum Altitude when at cruise altitude and Airspeed versus Weight on Approach. In some ways you could refer to the gentle rocking left and right as a sort of Stall Warning. The info from the documents in the 707perf.zip file are vary somewhat from the Captain Sim 707, specifically Max Altitude at the stated weights. I fly about 1000 feet to 2000 feet below what those docs say and the rocking issue doesn't happen.

Mark