1998 Chevy Cavalier Shift Problem

I have a 1998 Chevy Cavalier with a 130,000 miles on it. I have never had any problem whatsoever with it. Today the check engine light came on then I came to a stop when I pulled off it is not shifting right. It reves up then shifts into 2nd gear hard then each gear after also shift hard just not as bad. I have never had any shift problems. Is there a sensor that controls time of shift, or is it a vaccum line. Any help would be great, thanks.