2002 Chevrolet Impala Occasionally shifts Hard

My 2002 Impala 3.4l sometimes starts shifting hard through all gears. It’s not all the time. I have heard of others with this same problem and a transaxle service is apparently not the fix. Any ideas?

Ask around among people that you know for a locally owned, independent transmission shop - not a national chain shop and not a general mechanic - a local, transmission specialist. Tell them what is up and have it scanned for error codes.

How many miles are on this car and what has been done with it in terms of transmission service?

90k miles now and was serviced at 70k. The fluid looks great and this car never uses a drop.

What needs to be done is first scan the computer for any codes, then line pressure needs to be checked with a scanner attached to check the operation of the PCS (Pressure Control Solenoid) The PCS can be controlled by the scanner while monitoring line pressure. That is, only on a scanner capable of that particular fnction. If its shifting hard in all gears, the PCS is a likely culprit. Checking it like this could also point to other faulty controls such as a TPS (Throttle Position Sensor).