Hard shifting tranny

I recently bought a used 95 GMC Sonoma extended cab pickup truck (4 X 4). I have noticed that after driving it and warming everything up that the transmission shifts hard between 1st & 2nd gears. I have noticed
the fluid is a little overfull and appears dirty. Does any one think a dirty filter is the cause of the hard shift. Or is there an accessible part that can be replaced when I have the pan off to change the filter that is obviously the cause. It also has the 4.3 vortec. Auto transmission and A/C.
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Dirty filter affects line pressure / could cause hard shifting. Worn trans fluid [ thermal breakdown ] could do the same. Trans service is cheap insurance against rans failure.
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Paul wrote:

Thanks Paul,
You confirmed my suspiscions. I changed the filter and fluid today, I also added a quart of slick 50 tranny treatment. I've driven it twice today. The first time there was an immediate improvement. The second time was even better. I suspect the new filter is cleaning the remaining fluid in the torque converter.
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