I want to find the name of a terrible movie I saw (so I can buy it)
about 5 years ago (made in late 80's/early 90's) about a young black
man/boy (aged about 20) from the inner-city in new york or
philadelphia who travels back in time to the the 1850's or so to
experience slavery.  It's really bad, but I really want to see it for
some reason.

Hello.

I believe that your movie is "Brother Future" (1991).

"A young street rapper is transported back in time to the pre-Civil
War South, where he finds himself in the middle of a slave revolt."
source: Internet Movie Database
http://us.imdb.com/Title?0264441

'A modern-day teenager "travels through time" and finds himself
captured by slave hunters and sold on the auction block to a
plantation owner who forces him to pick cotton. He learns valuable
lessons about freedom and self=determination.'
source: cduniverse.com
http://www.cduniverse.com/productinfo.asp?PID=1555084&frm=sh_google

VHS copies are available from Amazon.com
http://www.amazon.com/exec/obidos/tg/detail/-/6304771010/

search strategy:
vhs, slave, teenager, time 

I hope this helps.

Perfect answer, timely too!