Paging Dr. Diesel

[perchance]

I'm out of hair to pull out so I'm throwing this open to any and all knowlageable diesel doctors.
The problem is over fueling of an Isuzu c240 with a kiki inline injector pump. The thing starts and idles like a champ and will rev to specified rpm but anything over idle and it lays down a smoke screen like a destroyer. In gear it will not exceed 1000 rpm. The injectors were pop tested so that ain't it. The pump was rebuilt and has no hours on it and when first installed it performed beautifully but the following day was when the touble started. I suspect something came adrift inside the pump but for the life of me I don't know what it could be.
Has anyone encountered this problem and if so what was the solution aside from the obvious "throw the effing thing overboard and get a new one"?