C-15 sounds like it is running against the jakes on low

Hey guys need some help. I have a c-15 mxs that I put back to a 6nz ecm the truck runs good but when your going up a hill and down shift and get back into the throttle it sounds like you are running against the jakes on low. After a few times of letting of the throttle and and getting back on it it takes off just fine. Thought it was an intake valve actuator sticking so I backed them all the way off since they are not being used any more but that didn't help. Any advice?

 

No jakes are turned off when it does it. Thinking maybe its a bad injector on the mechanical side. I'm going to hook my computer up and take it for a drive and see if I can get it to do it and do a cut out test. There is no codes or anything logged in the computer.