transmission clunks into third

99 Envoy with 74k. It has a clunk when shifting into 3rd. All other gears shift smooth. The lower the throttle the louder the clunk. No codes. 5k ago, I changed the fluid and filter with no improvement. It's been doing this for a while. Runs fine otherwise, the clunk is just annoying. Any suggestions?

Anyone have any idea as to why it will shift hard from 2-3? It does it warm or cold. Maybe the clunk is just my u-joints. I haven't changed those, but if the tranny is shifting hard at 2-3, wouldn't it just wear out new u-joints? Any thoughts?

First you have to make sure its either your u-joints, or your tranny. In my opinion, if its just the 2-3 shift, it probably is not your u-joints(but check). If it is the tranny(most likely), GM used plastic accumulator pistons in these transmissions. These plastic pistons have been known to break, or crack, causing a malfunction, or, in your case, poor shifting. In your case, its most likly the 2-3 piston that is cracked or broken, causing a bad 2-3 shift. To get to the 2-3, the valve body has to come off, and the piston is at the bottom right. Rebuilders usually replace these pistons with aluminum pistons(as the earlier models had), eliminating the chances of a broken plastic piston.

Thanks for the info blazes. Anyone know where I could purchase a 2-3 acuumulator piston? All I see on rockauto is a rebuild kit with 1-2 and 3-4 pistons.