'91 325I Transmition problem

help ! I am new here looking for some advice. I purchased a 91 325I for my daughter to use back and forth to school. The problems started about 3 or 4 months ago. while underway, The transmition would act as if you put it into neutral (it is automatic). If you stopped and cut it off / waited a few minutes, it would pull again for a short while. My mechanic pulled the transmition, replaced some clutches, inspected the valve body and other significant parts and put it back in. Our problem since then has been that the transmition, when cold, will not shift from 1st to 2nd gear before 5K. After the first shift, the thing seems to do just fine, it is just the initial shift that has the issue. numerous times he has pulled the transmition, checking the pump, o-rings and such with the same result. I know that he is going in the hole trying to help me, I am hoping someone can give me some information to help him find out what the trouble is.