Should I have the tranny completely overhaul or switch to another vehicle?

What is your question?

When starts , Slips High sound and moves slow until picks up speed. Trans oil was added several times improved shifting gears for some time began to smell like burning oil. The mechanic told me not add Trans oil anymore. Some leaks.Thank you in advance for your answer.

What makes this problem better or worse?

It's worse when running for more than 15-20 minutes

How long has your 2002 BMW 325i had this problem?

About two months started , but getting worse