transform 3 car garage to 2 block wall construction
 

I have a 3 car garage, the garage in cinder block construction. It is detached from the main House. I'd like to remove the center bay and make the 2 outer bays larger and add an access door in the middle. What should I be concerned with in doing this project?

Be concerned about the center bay being a load bearing wall.

That was my first concern. There is only one column of block on either side of the center bay before the outer two bays begin. There is also one top row of block above the middle bay(Tall truck bay) whereas the outer bays have 4 top row of block before the the roof begins. I should consult a contractor first shouldn't I?

Yes
 

Without a picture or actually being there, you should get some professional advice first that can see it firsthand.
A reputable contractor or an engineer will give you the best advice for your situation.
Then if you want to DIY we may be able to give usable advice.:D
Let us know.:)