2005 gls 1.6 auto. When at operating temperature, vehicle slips going into overdrive and gets stuck in 4th gear. Have replaced all recommended sensors input/output transmission speed, vehicle speed, tranny fluid is full and not too bad, thinking of draining and switching out fluid since not knowing what the previous owners used for transmission fluid and read a lot about non- hyundai fluid causing the same issue. At a loss honestly, check engine light will stay off after battery disconnect UNTIL it does its lurch when downshifting from OD to 4th to accelerate. When it shifts rough, it won't go…
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