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You are not clear.
Are you telling us the engine is at 4K and the car stops while the tach says 4K??????????????????????????

If YES, then the shifter bushing is suspect and the car is actually in N..that expalins the 4k, as there is a rev limiter in N and P for torque Converter protection. Try moving the shifter a bit on each side of N...........

or do you mean you stick it in N to keep it running and can't get it past 4K in N...that is the rev limit too, but the diagnosis is different ..maybe reword it ...

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A Dalton