acceleration stumbles unless throttle is feathered

[itsallhistory]

I have a 91 Sub V2500 5.7. I just replaced the engine with a boneyard unit. When out driving it runs well with one exception. I have the be gentle on the throttle or it will hesitate and seem to miss until I get up to around 50 mph. If I feather the throttle it doesn't do it. I put new plugs in it (gapped at .45), and I put a new EGR on it as well. Any thoughts on what it might be? Thanks.

 

[Boone83K10]

Vacuum leak

 

[itsallhistory]

I'll check into it. Thanks.

I also heard the 87 - 95 TBI motors are really picky when it comes to EGR valves and that the best way to get the right one is to go to the dealer with the VIN. Anybody know if that's true. I went to Oreilly's and got the BWD part that was listed for my Suburban.