hard clunk in reverse??

Old Vart is correct about them not filling the converters in park. I have seen a few torqueflites clunk when going into just reverse though. I can't say what causes it though. My 93 Dakota did it slightly and my friend's mom's 78 Diplomat did it real bad. In my Dakota I installed a Trans-go shift modifier kit which included a different manual valve that allowed it to fill the converter in park and it cured all the problems associated with reverse along with making it shift allot better. Man would it turn heads when it slammed 2nd gear.

Now you say yours don't go into reverse until warmed up. If I read that correctly that is more than just filling the converter. Filling the converter just takes about 30 seconds or so after placing the car in gear. If it takes longer than that to get reverse it's time to drop the pan to inspect things.