91 cavalier torque converter

I have a 91 Chev Cavalier and the torque converter locks up at 27 miles per hour when I am driving with a light foot. Do all Cavalier do this? If not, what is causing this problem? With the torque converter locking up at 27 miles an hour, the engine luggs and I have to step on the gas to unlock the torque converter. I can't figure out what is causing this problem. Does someone out there know?

Ron