99' chevy venture bucking

i have a 99’ chevy venture. lately, after driving 15-25 miles the vehicle seems to kick hard when it shifts. then, when it cools down and you go again it won’t do it till you travel 15-25 miles. i had tranny filter and fluid changed but it didn’t help. mechanic said he found no shavings in the tranny. does anybody have any idea what making it shift so hard after it warms up?

You need a specialist mechanic. Take the van to a transmission shop for diagnosis/repair.

You may have a worn pressure control solenoid fault in the tranny.

When my 2000 Silhouette started harsh shifting, I had the fluid and filter replaced and luckily that cured my problem.

The tranny shop (independent) owner told me that he has worked on a lot that required a new solenoid.

thanks hellokit and Roadrunner, at least you gave me an idea of what it is.