Trans. shifts hard only after driving awhile

Orings on the cluctch pistons are hard and flat. Changing the fluid may help soften them. I dont recomend any additives.

The filter and transmission fluid needs to be changed........The transmission filter is dirty and causing a flow restriction under load.....Hope this helps.

did you change the coolant temp sensor and the air temp sensor. sounds more like the coolant sensor is not working right this could cause the computer to dump more fuel which would cause a rich burn and the shifting problems check the leakage on the trans.When was the last trans fluid change and filter?

There are a set of pressure switches located on the valve body inside the trans pan,you could have them cleaned replace the filter,and then have the trans flushed.If this doesn't help you will have to have then trans checked for a pressure problem or leaking seals

It has nothing to do with the transmission, it's your engine mount thats bad.

A reason for hard shifting could be a problem with many things with various degrees of seriousness. It could be your ATF( automatic transmission fluid) is low or broken down and old. This would cause the hardness and the reason for stop and go traffic effecting it. Another possibility is your transmission is just shot, and the timing gears inside are worn and not properly shifting at the correct RPM causing a **** during shifting.

Some possibilties, not all!

~Lucas

Sounds like either the lock up converter or solenoid that operates it is "going away" Which trans is in it? I've had a similar problem (just the thump) In an aw4 trans in a Jeep, which I've isolated to those two components but it's too damn cold out to do anything about it yet!!! If the converter is staying locked, vehicle will be sluggish on starts from standstill when this is happening.

This is a common problem on some GM cars. There is a pressure control valve in the side cover of the transmission that needs to be replaced. The transmission does not have to be rebuilt. You will need to get a side cover gasket also.

any codes? the trans computer will store them. also the engine computer this is an obd2 car autozone can scan for free

Yes the computer uses TPS (throttle position sensor) and VSS (vehicle speed sensor) sensors information as well as fluid temp and other factors to determine shift points based on the info stored in the PROM (memory) IC chip, if it is not shifting then you either have a poor connection at the trans case electrical connector or a sticking shift solenoid inside the trans, I would pull the trans connector off and make sure it is clean and properly installed, look for a broken connector retainer as well, this is very common and can cause a loss of signal from the PCM (power train control module) module to the transmission shift solenoids. Most likely the 3rd gear shift solenoid is sticking off from sitting so long, had this happen on my truck, cleared itself.