More things to consider... how did this engine run BEFORE it went into this truck? If it ran fine before it went in here, then it is something to do with the chevy chassis or something to do with the mods you did.
Did you turn the full fuel screw the CORRECT way? Did you ckeck your air filter as I recommended in my first post? Is that K&N filter over oiled or dirty? Are you running this through the stock CHEVY air filter system??? If you are, then that is definitely a contributing factor to your performance troubles. Dirty fuel filter?
The solution to this problem has got to be simple, and the answer must already have been suggested. Remember the three important combustion engine factors... Air, Fuel, and Ignition. If you already have checked the 1) air source and piping, 2) fuel condition, pressure factors and hardware, and 3) the timing, then it HAS to work. There is something that was not checked, assumed good, or was overlooked. You have all of the answers in front of you and all of the wisdom you need right here.