Where are you getting your used engines from?
Get them from a local engine recycler that pulls used engines from yards and such, last one i had was check over and ran before put in my car, had 40,000k on them.
Who is installing them?
A person who used to work at a pontiac servicer before they are closed and now works at a dodge service center.
Are you using anything off the old engines for the new one such as the heads/SC pulley etc?
As far as i know the heads were from the used nothing was re-used engine wise.
Are you scanning?
As in scan gauge(aeroforce scan gauge) no i haven't gotten one yet. I hear about scanning your car but mine is stock what would be the purpose of scanning a stock engine.
Are you 100% sure all the sensors are functioning and giving you accurate readings for example temp sensor?
How would i tell if they were working "accurattly"