Transmission Clunk!

My transmission is shifting hard and clunking once in a while-but not all the time. I changed the fluid and filter a couple of months ago and that seemed to help but now it is shifting hard again. I thought I might try some seafoam cleaner and then drain and refill again. Any advice?? Thanks!

My van was doing the same thing quite some time ago. I did everything you did like change the oil and filter. What the problem is, the torque converter clutch lockup solenoid is failing. Your van has probably thrown a few codes too for this. I took mine to a dealer to see what my options were. They said they could fix it for $1100 when I can get a reman for $1600. I guess the transmission has to be removed to repair. I drove mine that way for years after that. I figured if it still moves and shifts, drive it. Like I said, I drove it for many years and kept changing the oil because it heats it up more and turns it dark. When my motor went out, I then bought a reman motor and a reman trans and put them in together. Now I have had no problems for 60,000 miles. My motor went out due to the dreaded intake gasket failure that these motors are common for. I say just drive it and change the oil. Maybe not take it on a long trip like on vacation. Unless you have spare money and time, you might as well get a reman from GM and swap it out. Whatever you decide, good luck.