Tranni gone??!!

I have a 91 Corsica with the 3.1 engine, which I use as a race car on a dirt track. On last race however, tranni did not shift anymore out of first gear when I hit the accelerator. Only when I totally lift the acc. pedal, it appears to shift in overdrive, but as soon as I hit the gas, it goes back to hi rev.
Any suggestions? :crying: :banghead: :screwy: