http://bimmer.roadfly.org/bmw/forums/e32/
If you register you can do a search. The transmission on the 740i has many problems. The most common is the valve body. It has 2 plastic balls that float in a maze of tubes and are suppose to be too large to fit in some areas. Since they are plastice however they eventually will fit in the are they are not suppose to. Some common symptoms are it will run in * fine, but won't shift in E. Reverse does not work. Or will not shift or go in reverse, but once warm will work or after I stopped and restarted the problem went away. I am not sure if this will help you, but I am sure someone on the roadfly board will have had a similar problem as you.