Replaced the motor about a month ago in my 88 2500 with a 350 tbi from a suburban, not sure of the year. Before the swap the truck ran absolutely fine no stumbling at all, i used the throttle body, distributor and all sensors from the original motor.
Now the truck stumbles and bucks with barely any throttle, but it picks up and goes fine when i give it about 1/4 throttle. I So far i've rebuilt the throttle body, checked for loose connections and vacuum leaks, replaced the fuel filter, checked the cap and rotor, and the plug wires are pretty new. Im at a loss for whats causing this. I also pulled code 43 but that should have nothing to do with a stumble... Any help would be appreciated

 

Heres a video of whats happening, last part shows just how much throttle i was giving it

 

Well i have a sort of interesting development in this case. Tonight I decided to hook my scanner up to the truck, i stated the truck it ran for about 8 seconds then died. I started it again this time it ran but it developed a miss. Now the really odd part is that the stumbling for the most part disappeared after the scanner was hooked up. I am beyond confused at this point