Transmission Problem

My Step Brother has a 1994 Chevy S-10 Blazer with a 4.3L V6 Automatic and the Transmission isn’t Shifting Right what could be the Problem?

Any number of about 100 things. Or more.

How about telling us a little more. How many miles on it, when was the last time the transmission fluid was changed?

[i] the Transmission isn't Shifting Right what could be the Problem?[/i]  

Maybe we could guess better if you could tell us how is it not shifting properly?