Transmission Service on 2005 Buick LeSabre

What is the difference between changing the transmission fluid and a transmission flush? Which is the best to do for the car?

Asked by for the 2005 Buick LeSabre
A transmission hydraulic system can hold a lot of fluid, say 13 quarts for your transmission. If you drain and fill the transmission fluid (Fluid Change), it may replace 6 or 7 quarts, therefore leaving 5 or 6 quarts of old/dirty fluid. Flushing the transmission removes all 13 quarts of dirty fluid and replaces it. I like the flush because it removes all the fluid. I don't suggest any additives, and neither does most of the vehicle/ transmission manufacturers.