LS Swap help please

[Caleb]

so im trying to get this dang thing working but i have no avail. its a 5.3/4l60e in a 86 k1500. it starts revs to about 3-3500k on its own and falls to 400-300 rpm for about 15 seconds before it dies. if i feather throttle i can keep it alive.cleaned TB cleaned intake and replaced gaskets to make sure no vacuum leak. im stumped i need this ready before college. im about to just take it somewhere and let them take my whole life savings. any advice would be great. im out of ideas. it does throw p0030,p0036,p0050,p0056. which are o2 sensor heaters i think. brand new sensors so idk? i bought this motor "ready to run". i also hear an occasional popping like noise from under the intake.