Joe Dumars sold his stake in auto supplier Detroit Technologies to Earle Higgins, another local-area baller who briefly played for the Pacers when they were ABA.

http://www.basketball-reference.com/players/h/higgiea01.html

I read this from Crain's, haven't seen it online apart from the link below which
requires some kind of membership fee or doing something illegal:

http://cdstage.us.publicus.com/apps/pbcs.dll/article?AID=/20060904/SUB/60901032/1033

Just in case you were worried about Dumars not having other business distractions besides being Pistons GM:

JD is slated to be on the board of directors for Strategic Bank of Michigan, a new (or maybe under new management) bank that's focusing on "small and midsize commercial loans and home mortgages".

And, Dumars Travel, his wife's business, had ~$20 million in revenue last year, making it one of the top female-owned businesses in the state.

sounds like Joe D and Mrs. Joe D are doing well outside of the NBA. nice.

He just recently got on the board of Oakland Family Services, too:

http://www.oaklandfamilyservices.org/press/2006%20Releases/NewBoardMembersPressRelease.pdf