Champion 720 w/ clark power shift seems to be shifting hard

Hey there, thought I'd bounce this one of you guys and see if you have any ideas, haven't had much time to delve into the book yet, but my 1980 720 (with the 3 speed clark power shift trans) seems to be shifting into forward and reverse with a clunk the last 20 hours or so. I've had the machine for a few years now and have put a few hundred hours on it, and don't seem to remember it doing this before. When it goes into forward or reverse, it just seems like theres a clunk to it, like to much engine speed, but as far as I can tell everything is normal there, any ideas? I changed the fluid (atf) about 150 hours ago, and the filter, and replaced a hose on the filter housing to the torque converter. Once its in gear (forward or reverse) it seems to be normal, just from neutral into gear I notice it doing this. Any ideas? thanks in advance