acceleration from stop trans shifts immediately into higher gear

My 1998 Buick Regal GS upon acceleration from stop, the transmission instantly shifts from 1`st gear into 2`nd or 3`rd. What may be causing this? I have changed the fluid & filter, this did not help.This problem is intermittent. Anyone have any ideas for me to try?

Any ideas would be helpful.

Thanks; rlh41

i have a 98 grand prix gtp that did the same thing. it was a speed sensor in the tranny. i would get it scanned to see for sure tho.