I have a 1990 full size blazer with a rebuilt transmission, last week it started not shifting out of first gear when it was cold but after going about a mile it worked fine. So I did a filter/fluid change and it didn’t fix the problem. So I took it to the transmision shop where I was told the problem was in the valve body. Four hours later they changed my fan clutch and said with 100% certainty that it was the cause. The next morning it still would not shift. Once warm it does shift much earlier and smoother than it did before. Did the fan change the shift pattern or was something else adjusted? (this shop is who rebuilt the transmission but it is not under warranty)
That fan has nothing to do with your transmission problem. Now, if you were having problems where the transmission was running too hot then I would say yes, a fan not operating properly can and will cause a transmission to overheat. I’m leaning towards possibly a governor problem, sticking maybe. Have they looked at that? I would just love to hear their explanation as to why they think a fan clutch would be causing your problem.