I have a 1989 300e with automatic transmition that shifts smooth through all gears until i go about 30 miles and the tranny really warms up. Then it doesnt want to shift into 4th gear (drive). When I get to 40 to 50 mph I put it into neutral and quickly put it back into drive it usually will shift into drive. After the car sits and cools down then it shifts fine again until it gets really warmed up. I just had the tranny drained along with the converter and put in new oil and conditioner to see if that helped and it shifts really smooth until it warms up. Any suggestions?????