Cadillac Repair: overheating, bolt holes, head bolts

Question
hello,ok i was told by aamco repair shop  i needed an ecm for 94 cadillac concourse deville , it took them 2 weeks to figure how to do it, then i paid them 500 dollars and got it and it was overheating i had it towed to dealer  2 days later  they said radiator was busted  they replaced, i went to pick it up and got 1 mile down road and showd on display engine overheating stop engine? I  let it cool off then did not want to start ,  finally got ti started  and  still overheating took back to dealer they seemed to be frustated with me after i gave thm 640 dollars ! it is at dealership repair shop now , what could be the problem and what do i do  after they  gave me  reason for issue and repaired it,without getting ripped off/ please help  just want my car back

Answer
What was the first places reason for replacing the ECM ?.

The second place should have know that this particular year vehicle with this engine has an extensive history of bad head gaskets due to the well known cause of the steel head bolts tend to tear out the head bolt threads in the engine block and there was a manufacturers service bulletin given to ALL Cadillac dealers advising them of this very very common problem and the only fix is to drill out the head bolt holes to a larger size and install heli-coils in every head bolt hole in the engine block and install different head bolts.