I recently had to replace the PCM in my 96 Bonneville to fix a high idle problem. I called a local salvage yard and was able to buy a PCM that came out of the same year Bonneville and I did not have to have it reflased. It fixed my problem and I was very happy. He just wanted the old one back.
When I first called the yard, he was going to sell me one out of a 96 Monte Carlo which meant that I would of had to have it re-flashed. I called the local Pontiac dealer and he quoted me $70.00. Luckily when I called the yard back, he was able to find one out of a Bonneville.