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Discussion Starter #1
I am experiencing intermittent hard shifting. This happens periodically. Otherwise the transmission works perfectly.
 

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When was the last fluid/filter change? If not recent, consider one. Do you have the 4l80?
 

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Discussion Starter #3
When was the last fluid/filter change? If not recent, consider one. Do you have the 4l80?
Fluid changes 10,000 miles ago. Was doing the same thing before and after fluid change. It is a 4L80 transmission.
 

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Check your fuel pressure as well. The TPS tells the computer when to shift based on speed and throttle position
 

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Throttle position could be your problem.
Roughness in the throttle position sensor can cause harsh shifts.
 

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Check your fuel pressure as well. The TPS tells the computer when to shift based on speed and throttle position
This was my the cause of my problem on my 93 C1500 with a 4L60e. I had hard, late shifts and a bit of idle fluctuations. Fuel pressure was marginal @ 10psi. Replaced fuel pump and got 13psi and hard shifts went away.. smooth again. I assume because I had to use more throttle than normal for given speed/condition the PCM thought I was trying to accelerate hard when I really wasn’t.
 

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That's exactly the issue, Sabino. The TPS level is assumed to be delivering some amount of fuel that is X, but with a marginal pump, it is some percentage less than X and it starts to behave badly
 

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If you have an outboard fuel filter, replace it. It could be clogged.
 
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