Truck hesitates (won't pick up speed) while driving on 2005 GMC Savana 3500

Good day, i had asked some questions about this problem before and since then i have change some parts.

I have it worked on by a gmc master tech. with over 16 years experience. He diagnose it and told me that it needed a tune up and he did it. parts change (5 new coil pack, 8 ac delco spark plug and wires). He flush the fuel system and take out the injectors and check them for the right psi.

Over $1,000 dollars later and the problem still exist.
The hesitation is not as much but it still happen. One minute it will fight to pick up speed then the next it drives fine.

ANY Suggestion?

check fuel pressure
The Mechanic did, but one bank is not getting enough fuel (cylinder 2,4,6,and 8 are getting the right psi, but cylinder 1,3,5, and 7 is not getting sufficient fuel). ANY IDEAS; PLEASE HELP.