What Ed said. The few that I've cut open look like they failed were they sit most often, aka at cruise. Unfortunately, they are fairly well sealed. I was never able to "clean" one without opening it up. But the chance of it being "just dirty" is very slim. I was only able to save one.

 

The problem with the "pot", "pressure switch", or " resistor pack" fixes is they only give you a fixed speed shift point. The TPS gives a varying voltage to the PCM to control when OD comes on, or off (passing gear) for that matter. The more throttle, the greater the delay until upshift.

 

Brake cleaner that leaves no residue. I don't have one of those automagic things so I've never dealt with the TPS so I'll defer to the experts on how it's constructed. The fact that the wiper wears in one spot seems correct however.

With the old radio pots in the past I had some luck rubbing the resistor surface with a pencil to restore them.

Edwin