+1 on what Johnny said. Transmission fluid should be red, not brown. Hopefully a fluid and filter change will help with the problem and not cause more issues. Transmissions that have lived with the same fluid for many years become happy with it, and changing to new fluid can cause additional problems. The high detergent in the new fluid tends to clean the inside of the transmission, and while I don't know the exact reason for it, I've seen it cause problems on more than one vehicle with fluid as bad as yours is. Typically in a case like yours it would be wise to not change all the fluid at once, but to drain and replace a quart or two at a time over the course of several months so you don't shock the transmission. As weird as it sounds, I'd reuse about half of that nasty old fluid that you removed, replace the rest of it with Diamond SPIII compatible fluid, and drive it with my fingers crossed and lucky rabbit's foot dangling from the rear view mirror.