I wouldn't think that would be related to the automatic transmission. Its easy to see if you need transmission fluid. Pop the hood and check it. There is a dipstick that goes right into the transmission. When you check it, make sure the engine is cold. The fluid should be a pinkish color (some may be different color) and check to see if its at the right level (markings on dipstick). If it is, then you got another problem on your hands. If its a dirty color, then you need it changed.
Another culprit to stalling is Mass Air Flow sensor. It was a recall on 2000 Elantras for stalling. Eventhough yours is a different year, it could be it as well, although your engine is the 1.8 and not the 2.0. But I would have that looked into. It could also be fuel filter or just something clogging the line to cause it to stall. Does the car idle low, then try to bounce back up and then stall?
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2000 Hyundai Elantra GLS (Photochop)
-PIAA 1100 series driving lights
-PIAA Plasma Headlights
-10" Pioneer sub powered by Kenwood 600 watt amp