I've 2 suggestions, both to do with transmisison fluid. #1 - check fluid level according to the manual. It's normally done while the transmission is warm, engine running, in park, check the dipstick and ensure the level is around the "full-hot" level (there should be 2 levels markers on the dipstick, cold low/high and hot low/high). If it is low, add small amounts of the recommended transmisison fluid (again, check what grade, should be in your owners manual, maybe Dexron 3)? Suggestion #2 - drain and fill with fresh fluid. You'll only be draining and filling about third/half of the contents of the tranny each time, may take 2 or 3 drain/fills over a period of a few days to get a majority of fresh fluid in the transmission. Not all of the fluid drains when you remove the drain plug, some remains in the torque converter.
Final thought - if draining or adding transmission fluid - ensure you're draining and filling the transmission, not the engine. Don't mix the two!!