Automatic Transmission

Hello, I Took My Car To The Mechanic In Order To Change The Engine Gaskets, So The Mechanic Took Off The Transmission To Do The Job And Then Put It Back On. After That, Sometimes (not Always) When I Put It In "d" It Starts In 2nd Shift So I Have To Put It In "l" And Back To "d" Again To Solve The Problem. The Mechanic Told That Often Happens Because The Transmission Was Never Service. My Fear Is That He Did'nt Put Tha Transmission Back On Correctly. How Can I Tell?

Well if it worked properly before I would take it back and tell him to fix it. I have never heard of that happening. Perhaps he didn't plug something in or broke a spring somewhere????