Use ATF +3 and change it every 10,000 to 15,000.
Some shops are now recommending a quart or 3 of mobil 1 synthetic in the trans also. It saves the OD planetary since it runs the most and needs a good lube.
This usually starts some flames, but I have used 2-3 quarts in a torqueflight A-500 for 70,000 miles and over 7 years. The pan is clean every time it gets changed. The trans works great.