大道理不懂也不熟悉你的車，隻是出於好奇做了些功課，網傳的一種說法覺得有些道理

1：In/out shaft speed sensor fails: Cheap fix if possible but most likely I will do first.

2: Rebuild tranny: May not worth go ahead expect you can make it.[fluid/solenoid/seals]

3: O2 sensor related can easy fix with swap test if you wanna save manoy!

My 2c

Quotes:

http://www.justanswer.com/hyundai/6nxe3-hyundai-santa-fe-code-p0733-p0734.html

http://www.hyundai-forums.com/lc-2000-2005-accent/74032-engine-check-light.html

http://www.hyundai-forums.com/cm-2007-2012-santa-fe/433489-fault-codes-p0733-p0744-stuck-3rd-gear-3.html

http://www.carid.com/2007-hyundai-sonata-transmission-solenoids-sensors-switches-control-units/

以上資訊僅供參考，年代車型等可能並不和你的一致,不過去你這個車型的論壇應該能有比較多的信息。