I have a 1988 LTD Crown Victoria with a Ford AOD transmission. The transmission slips in overdrive. This was probably due to a TV (throttle valve) cable problem–the plastic grommet holding it to the throttle broke. This has been fixed with the correct brass part and the transmission seems fine as long as I simply leave it in Drive.
The question is how long will the transmission last. Is it very likely to fail shortly or could it last for years? (I am wondering about taking it on long trips.) I have no interest in having the transmission rebuilt.
I’m not a transmission specialist, but I question whether a TV cable issue would have led to this problem. My understanding is that the TV cable position only affects the shift points. I would think that the slipping in overdrive is due to a faulty/worn clutch, band, or control valve.
Regardless, it’s hard to predict how soon things will get worse, but I would assume sooner (weeks or months) rather than later (years) with respect to 4th gear (overdrive). For the other gears, though, it could go years before a problem develops there. Just use it as a three-speed transmission – turn off or don’t shift into overdrive.