My automatic transmission sometimes shifts into over-drive and sometimes it doesn't. It usually shifts to over-drive if the car has been parked for several hours, but after about 4 miles, it will not shift into over-drive again, or every once in a while. An Aamco shop said I need to have the whole transmission repaired for $900+. I have read that there is a computer chip that might be malfunctioning. Should I get a second opinion or have a dealer check it out? My car is a 1991 Mercury Tracer, 4 cyl.
Thank you, in advance, for your response.