Transmission problem
1997 Mitsubishi Galant 4 cyl Two Wheel Drive Automatic 20000 miles

my 1997 galant seems to now have a variety of issues. when the car is cold and i put it in reverse it nearly dies, then rev's back up again and repeats this cylcle of few times. while im driving i can feel the transmission slipping when it is downshifting, and when the happens more often then not the car will turn off when i stop at a light or stop sign, or if it dosen't die it will come very close to it. these thing just started out of now where and i really don't kno what it is. i brought to a mechanic and they check the transmission oil level and it was fine. they refered me to a transmission specalist, but when he test drove the car it worked fine, so i guess this only occurs if the tranny is cold, but either way it is a problem, got any idea what it might be??