My engine kicks when the revs fall below 1,500 revs. on 1999 Ford Escort

I live on a narrow windy track and drive mostly in 2nd gear until I get to town. When I slow down to go round a bend the revs fall below 1,500 and the car won't pull away up the hill with out the engine jumping. I then have to put it into first gear. It never used to do this. What is wrong with it?

Asked by for the 1999 Ford Escort