I recently experienced transmission(?) problems with my 1991 Explorer. A brief history of the problem: I had gotten used to the slow shift in the cooler mornings, but when the transmission began to slip I got concerned. I had the fluid and filter changed and the slip went away. I had confidence in the healing, enough so that the wife and I went on a short trip this past weekend. About 100 miles into the trip the transmission began to slip again and seemed to me to be hot. Another thing it was doing was stalling at intersections, kinda like the transmission was still working when it shoulda been resting. I then parked the Explorer for the night and rented a car to get to our destination. Upon returning the next day the Explorer did the slow shift thing as usual (reving to near 3000RPM before shifting) it did howevr shift and seemed to be doing quite fine so we headed home. After about 10 minutes into the return trip and after pulling a long but slow grade it began slipping again. This time however it filled the inside with smoke and left quite a fog on the interstate. The smoke was coming from some serious fluid loss out of the transmission. The Explorer came home on a wrecker. What could it be?? I would appreciate any feedback or suggestions as I don't have a lot of $$ to put toward diagnostics. The transmission is a A4LD according to the door jam tag.