if you lost all your fluid then your modulator valve has a blown diaphragm and is sucking the ATF through the carburetor.

 

Hi I dont know if you have corrected your issue. I had and old ford in my earier years that I swaped a 4sp to an automatic, with a similar issue. I found out the issue was my gear indicator on the dash was off. I would put it in "D" but really the trans was only in 3. A simply adjustment to the linkage fixed that. I found out by removing the driveshaft, chocking ALL WHEELS and parking brake on, unhooked linkage from trans, started up in neutral and shifted the trans lever one time and gave it some gas,,, it shifted all gears. that told me the linkage was not adjusted right. Indicator showed D but trans was really in 3rd.