Hesitation and stalling

Okay mechanically inclined friends, I have a
1990 c1500 with a 305 engine. It had this
problem where it would hesitate to the point
it would stall upon initial acceleration and
after it started to warm up it would do it
when it was idling as well. I swapped the
throttle body on it with one we rebuilt out of
a junk yard and the problem stopped. Well
we did more work to it and ended up
swapping the engine for one of the same
size. This took awhile and in that time dirt
dobbers crawled into the rebuild throttle
body ajd made a nest. We rebuilt the old one
with another rebuild kit and parts from the
one from the junk yard and put brand new
injectors in it for good measure. Well I'm still
having the same problem and I've changed
just about every sensor on the the dang
thing, even took it to a shop and they said
they thought it was the ECM. Changed that
and still the same thing. So now I'm at my
wits end with this truck and need some
advice or an answer would be nice.