Cruse Control Problem

I have a '94 Ford Taurus wagon, and when I set Cruse Control I find that it slips when going up hill, even small hills. Is this a problem that is common to the Taurus or is the Cruse defective and needs to be fixed? Also how expensive is it to fix?

Sounds more like a transmission problem to me.

What happens when you lock the transmission in third gear??

Manual or auto transmission? When was the last time the spark plugs were changed Months and miles), transmission fluid changed (auto) how many miles on the clutch (manual)