OD off blinking

[Longshot270]

My dad's '97 PSD F250 has been having a transmission issue for a while now. Ever so often the OD off light will start blinking and the truck will start shifting much firmer. That is all that happens until he unhooks the batteries and clears the code. The code reader he bought for the expedition doesn't pull any codes off the truck. His friends at work are saying because it has two computers, the PCM and one other (I'm assuming they are referring to the FICM) and because of this his code reader can't pull codes. He talked to a guy at a transmission shop and they told him that his TC clutch is probably starting to wear out. They said when the TC does a full rotation that it will trigger a code and make the light blink. This seems logical but, as I said earlier, no codes are available to make sure. He told me the guys at autozone said they couldn't pull codes because apparently they use the same unit. Is this common enough to buy a new TC and start throwing expensive parts at it without knowing for sure? The truck is not even touching a dealership parking lot. He has also been looking around at prices of new TCs and because of the directions of his coworkers he thinks he can just change it out in his garage after removing a few bolts. I'm getting the feeling that regardless of what his coworkers say, this is no easy task that can be done with just a pump jack, a set of wrenches and a change of ATF.

Thanks in advance for any info.