Ecm computer

If the donor truck had identical powertrain options and no model-year variations, the PCM would be good to go, but if not it will have to reflashed to factory specs to match your truck. Generally it's pretty hard to pick up a new chip from a scrap yard and have it work without needing to be reflashed. You can get that done at a dealer ($$$) or find a local mechanic or even parts store that can do it, just requires a GM scan tool, GM's web site can provide programming updates to your specific PCM that can be downloaded to your computer/scan tool then used to flash the PCM.

I am also having problems (different ones) after having my ecu changed; however, I came across this resource for reprogramming ecu's. Mine is a 1994 Silverado K1500, and it is not listed. https://www.aa1car.com/library/gm_reprogrammable_modules.pdf