4.9 ECM

I switched out my ecm with another one i got at the junkyard and it was
inside so there was no water damage. When i swapped ecms i could tell
something was different, it seemed to pull a little harder and it was
smoother on accel and decel. But the new ecm was really rough when
cruising down the alley in 1st going 5-10kph. And when its warm and idling
at 600ish the new ecm makes the cam a LOT more prevalent than the old
ecm did at idle. I checked part numbers for both ecms and they are the same
(161...something) and i switched my prom when i switched ecms. So why are
they different? is one bad? Oh and my old one (not junkyard) was
remanufactured and the new one is an original. Just trying to figure this out.