1995 sivlerado rebuilt engine problems HELP!

A friend of mine had a rebuilt short block installed in his truck this last week, the heads were gone threw and everything is new with the exception of the distributor and the throttle body unit. he and the guy that put the engine in cant seem to get it to run right it has a rough idle and spits and sputters under load trying to get up to speed. he said the scan tool they used said everything was running with in spec. and he had no check engine light coming on. any suggestions? any help will be appreciated!

anything?

Did he put the same engine in?  If it is a different engine are the cam, crank, and heads all the same?  If not the computer will think it still has the old engine in it and it won't run right.  It's somewhat like adding a hotter cam, you have to reprogram the computer.

it had a gopher rebuilt 5.7 L in it before and once again he went with a gopher rebuilt 5.7 L
 

make sure the wiring gounds are tight