My '93 ATX Sho w/ 127,000 mi, has started to have shifting problems... the problem started a few weeks ago, on the freeway coming back from LA, it would not shift out of 3rd into 4th. The OD light was working (going on/off with the switch) but the trans would not shift into 4th. I stopped the car and shut it off, after restarting it, it was fine. It has done this a few times, and now it has twice done the same thing with 2nd to 3rd gears. Coming to work this morning, it down shifted into 2nd on the freeway to pass, but would not upshift into 3rd or 4th. Last week, I frush the trans and replaced the filter... Otherwise the trans is fine.. Any Ideas????