1996 Yukon GT Massive Transmission Leak

Please Help! I have a 1996 Yukon GT, 4wd. I adore this truck and have practically redone it from front to back. about 3 years ago I had terrible transmission problems. Had trans replaced by a dealer in Brooklyn NY and truck has been great ever since. Dealer has since gone out of business and I now live in NJ. Have a great mechanic but I have a intermittant massive trans leak that no one can find. Put die in trans and looks like was comming from trans pan. You will drive truck for 2 weeks every day no problem then not use for 2 days and come into garage and find 5qts of trans fluid on garage floor. 7th time in one year, mechanic has no answers at this point, dealer can not find either. anyone seen such a crazy thing?????