Harsh downshift coasting from highway speed

Anybody have a hard shift decelerating from say 75 mph? Truck is a 2019 5.7 4x4 cm. 80k miles or thereabouts. I had traveled about an hour with a couple of small town slow downs but mostly at 60-80mph and had to do a couple aggressive downshifts to pass slow vehicles. When I came to my destination I let off the gas and it slammed from 6-5 then operated normally. I also just noticed general clunky shifting in town. Had the trans serviced at 60k and then topped off after I noticed clunky shifting after the service. They said it was not quite where it should have been. Anyhow the important thing here is the harsh slam of a 6-5 downshift. I've noticed it here and there and no rhyme or reason except usually after spirited driving on the highway.

 

I’m around the same mileage as you on a 2021.

What do you mean by topping off the trans fluid? Did you add more than the spec’d amount?

 

I had a drain and fill done. I noticed the bump shifting after that but I also moved to the city where you're on and off the gas more frequently so may have just become aware of that. Anyway I took it back in at next oil change and had them double check the trans and they told me that it was half or a quart low I don't remember exactly and that they had brought it up to correct level. Also this slam shift from highway speed is only on occasion. Just putting it out there to see if it's something to worry about or normal and not going to cost me 6k

 

my 2019 has shifted harshly since i left the lot. Sometimes it is so pronounced that it will splash your energy drink in your face.

It did it before I installed cooler, and after cooler. Admittedly after the cooler, on super cold days. it does seem a bit worse. I did a full fluid exchange at 46,000 miles and it helped a little bit.

It isn't repetitive at all but the drive cycle I've seen it do it most is 1) after some aggressive wot runs, one of the next few downshifts will be harsh and 2) when cold with moderate accel.

 

When transmission decides to shift, it asks engine to reduce power. It needs to switch gears within this power reduction window, otherwise engine recovers power and hard clutch engagement happens. Usual harsh shift culprits are low or high ATF level (too much ATF causes it to foam and become effectively less viscous), sticky solenoid in valve body and incorrect adaptation in software. Later you can fix by forcing TCM into adaptation mode and driving in a specific pattern. Transmission does not have a line pressure sensor that software can read, it relies entirely on preprogrammed pressure values, which differ on real hardware, especially with wear accumulating in valve body, or simply a subpar part was installed in assembly line.

Driving with harsh shifts is apparently very bad for transmission longevity.

Mine does 1-2 a bit worse then the rest of shifts, and only when cold. But nothing too concerning. Wife's 2022 Sequoia with same engine/transmission combo is butter smooth.

 

If fluid level is good, tune it out. Get an aftermarket tune.