Hard Shifting

I've seen a lot of posts regarding rough shifts like my 99 GLS (93k mi.) suffers from. Can someone explain why this would happen only in warm weather and stop and go driving and not when the outside temp is less than 60 degrees?

Knowing the above my eliminate some causes which will occur regardless of temperature. I don't want to fix something that aint broke.

Thanks

The problem relates to inconsistent operation of the pressure control solenoid, which affects shifting of the tranny. The colder temps allow thicker viscosity tranny fluid, keeping the shift more normal.

Once the temp comes up, the fluid will thin out and your problem will return. (Except during the first 20 minutes of operation while the oil is still coming up to temp.)

Thank you for a really sensible answer.

I had to add some "universal" transmission fluid after my service guy left it short. You think a complete fluid change to the proper fluid for GM cars will make a difference?

An oil change may help, especially if the current fluid is spent. I would recommend a bottle of Lubegard to go with it. That may loosen up some of the varnish deposits that may be contributing to the problem.

Have the vehicle scanned for engine/tranny codes.....not all codes turn the light on....

like said Lubegard dr tranny and tranny flush all by the same company can help But transmissions are meant to be dumped and new filter i think 60k other would know more i only got to engines in school and life try those and the other stuff the more knowledgeable people put in my tranny post

I read all of the forums and ignored my EXTREMELY hard shifting for almost a year. For me, it turned out to be the Mass Air Flow Sensor. Good luck.

thanks so much with how old and miles i will see how much a mass is and also do the flush and filter change thes computerized cars are to much lik pcs one thing can cause a whole host of problems that seem like five possible answers i miss the 70s and 80s less computer and other fancy crap and no matter the engine you could hop on the fender and have tons of room to work and dangle your legs lol i also found out these stupid fancy electronic climate controls on these cars have no vent feature just ac my ac is dead so it 4 windows man i miss older shit