changed numerous thins n van continues to spit,sputter n stall out!!

What is your question?

we have done a full tune up, changed fuel filter, fuel pump, throttle body gasket ,cadillac converter, map sensor, i know there is probably more but it runs like a heep still.. Back up, it stalls,, stop anytime and go to take off,, it stalls.. its popping and fartin and just sounds BAD! Sad thing is we just got it back from a mechanic.. What could it be?? Please help!