I have a 1997 2 door Cavalier, 160,000 miles, 2.2 liter. The automatic transmission will not engage in forward gears. It has no problem with reverse. I have changed the transmission fluid, and filter, upon doing so the car would run, but it was rough, in turn I replaced all spark plugs. Afte rwhich the car would not engage in the forward gears. Any suggestions?