I have a 1994 Mustang GT with an automatic transmission. The transmission does have a shift chip installed by previous owner and the transmission has shifted well for the last ten years. Now, when I put the vehicle in reverse, I can feel the transmission shift into reverse, however the vehicle will not move. The forward gears appear to be ok, at least driving through the neighborhood up to 30 mph. Fluid level is good and fluid is clear. Are there any fixes I can try short of rebuilding the transmission?