TH350 gone bezerk?

Hey. I was drivng around in my automatic 74 Nova, in D (drive), stopped at a light, and began down the next street. I get up to about 35-40 mph and the tranny won't shift to 2nd. Could it be tranny fluid? I checked it after diving it around (with the car on) and it was past "full". whats up? thanks.

- Nick

Gov. gear could be striped or Gov. could be stuck, Is there antifreeze geting into the tranny (bad radiator)