Coming home the other night my transmission (auto)started slipping, jumping in and out of gear and finally going up hill it would not pull at all and it smelled like burning clutches. After being towed home, 15 miles, it had cooled down I guess, I cranked the car and it pulled into the driveway. The next day my husband changed the filter and about 3 1/2 qts of transmission fluid,whatever was in the pan . we filled it back up and I drove it about 30- 40 miles without any slipping, but when I tried to back up reverse started slipping. The fluid looked brown and smelled burnt, no previous symptoms or problems, it started very sudden. Any ideas or suggestions or just get a new transmission? We thought we'd try a complete fluid change before putting it in the shop. Thanks for any help.