how are 3500 stall conveters sopasto act

Sorry but your friend is wrong about having to change the fluid after just 500 miles. there's a major issue with the trans. or it wouldn't have burned up the fluid in that short a time. I've rebuilt numerous transmissions (Mopars and GM's) over the past 28 yrs. and never once had to change the fluid after a short period like that. My guess is who ever rebuilt it screwed something up and it has the clutch plates and/or bands burned up already. Sorry to give you bad news but I just want you to be informed correctly.