hesitation under load

What is your question?

1) car stumbles at about 1500-2000rpm under load like its about to stall (sometimes does) also there is knocking coming from the valve train 2) does not happen in neutral 3) catalytic converters were replaced two weeks ago as were vacuum hoses (visable ones) 4) cleaned throttle body and removed debris from radiator screen 5) Air cleaner is in good condition