95 accent tranny shift problems

i have a 95 accent(automatic) that has a bit of a problem. if i slow down from any speed above 30 to a stop my transmission makes a hard thump like slamming into gear. it doesn't do this if i turn off my overdrive while decellerating. is this a problem with my tcm, or an internal transmission problem. ive had the car for a little over a year and it has done this since i bought it.

check your trans fliud hot in Neutral e- brake on where is the level and what color is the fluid when wiped on a white napkin?