Hello, I am John, a Ford dealer technician.
I hope I can help solve your problem quickly and accurately.
If when in od when it goes to shift into 4th gear it feels like it is going into neutral then you have a worn direct clutch in the transmission. To repair this you will need to remove the transmission and overhaul the unit. If the transmission is just sticking in 3rd gear and not going into neutral you have a sticking od servo regulator valve in the valve body and you will need to remove the valve body and free the valve up. It is common for the overdrive servo clip to break and jam that valve causing the problem. Have had several 04 models with this problem. If this is the case you will also need to replace the clip for the od servo. You will be able to get to this once the valve body is out.
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