i have had trouble with my steering whenever i am driving and i try to make a turn it starts to freeze up in mid turn and i have to use all my strength just to finish making the turn and my mechanic advised me to goto the local gm dealer and in turn he couldn't find the problem what ever it was doing it stop doing it for some reason and that was 5 months but started doing it again a few days ago. i am confused and outraged that none can find the problem for me. help! i am scared to have an accident.

Optional Information:
2000 Chevrolet tracker 4 cylinder

Already Tried:
evrything! my mechanic and i had it at a gm dealer on a machine an they said they can't find the problem.